Unit 2 Highway Development and Planning 1.0Types of roads 1.1 Based on usage This classification is based on whether the roads can be used during different seasons of the year. 1. All-weather roads: Those roads which are negotiable during all weathers, except at major river crossings where interruption of traffic is permissible up to a certain extent are called all weather roads. 2. Fair-weather roads: those roads, where the traffic may be interrupted during monsoon season at causeways, where streams may overflow across the roads. Fig: Causeway 1.2 Based on carriage way This classification is based on the type of the carriage way or the road pavement. 1. Paved roads with hard surface : If they are provided with a hard pavement course such roads are called paved roads.(eg: Water bound macadam (WBM), Bituminous macadam (BM), concrete roads) 2. Unpaved roads: Roads which are not provided with a hard course of atleast a WBM layer they are called unpaved roads. Thus earth and gravel roads come under this category. 1.3 Based on the type of surface provided 1. Surfaced roads: Surfaced roads are those, which provide with a bituminous or cement concrete surfacing 2. Un surfaced roads: un surfaced are those, which are not provided with bituminous or cement concrete surfacing?
Transcript
Unit 2
Highway Development and Planning
1.0Types of roads
1.1 Based on usage This classification is based on whether the roads can be used during different seasons of the year.
1. All-weather roads: Those roads which are negotiable during all weathers, except at major river crossings where interruption of traffic is permissible up to a certain extent are called all weather roads.
2. Fair-weather roads: those roads, where the traffic may be interrupted during monsoon season at causeways, where streams may overflow across the roads.
Fig: Causeway
1.2 Based on carriage way This classification is based on the type of the carriage way or the road pavement.
1. Paved roads with hard surface : If they are provided with a hard pavement course such roads are called paved roads.(eg: Water bound macadam (WBM), Bituminous macadam (BM), concrete roads)
2. Unpaved roads: Roads which are not provided with a hard course of atleast a WBM layer they are called unpaved roads. Thus earth and gravel roads come under this category.
1.3 Based on the type of surface provided
1. Surfaced roads: Surfaced roads are those, which provide with a bituminous or cement concrete surfacing
2. Un surfaced roads: un surfaced are those, which are not provided with bituminous or cement concrete surfacing?
1.4 As per the Nagpur Plan, the roads are classified as
i) National highways
ii) State highways
iii) Major District highways
iv) Other District Road
v) Village Roads
NECESSARY OF CLASSIFYING ROADS:- To plan a road network for efficient and safe traffic operation , and for knowing the clear information of a particular root in a country, the classification of roads is necessary.
a. NATIONAL HIGHWAYS:- These are the important roads of the country. They connect state capitals, ports and foreign highways. They also include roads of military importance. They are financed by the central government.
b. STATE HIGHWAYS:- These are the important roads of a state. They connect important cities and district head quarters in the state, national highways & state highways of neighbouring states. They are financed by state government roads and buildings department of the state government constructs & maintain these roads.
c. THE MAJOR DISTRICT ROADS:- They are roads connecting district head quarters, taluk head quarters and other important town in the district production and market centres with each other and with state & national highways & railways.
d. OTHER DISTRICT ROADS :- They are district roads of less importance
e. VILLAGE ROADS:- They connect villages with each other and to the nearest district road. They are financed by panchayats with the help of zillaparishads and state government.
1.5 Classification as per third Road Development Plan1. Primary System
a. Expresswaysb. National Highways
2. Secondary Systema. State Highwaysb. Major District Roads
3. Tertiary Systema. Other District Roadsb. Village Roads
1.6 Classification of Urban Roads
Arterials: It is a general term denoting a street primarily meant for through traffic usually on a continuous route. They are generally divided highways with fully or partially controlled access. Parking, loading and unloading activities are usually restricted and regulated. Pedestrians are allowed to cross only at intersections/designated pedestrian crossings.
Sub Arterials: A Street Primarily meant for through traffic on continuous routes, but offering somewhat lower mobility compared with the arterial roads
Collector streets: These are streets intended for collecting and distributing traffic to and from local streets and also for providing access to arterial streets. Normally full access is provided on these streets. There are few parking restrictions except during peak hours.
Local streets: A local street is the one which is primarily intended for access to residence, business or abutting property. It does not normally carry large volume of traffic and also it allows unrestricted parking and pedestrian movements.
2.0 Planning Surveys
Highway planning Phase includes
1. Assessment of the length of the roads required for an area2. Preparation of master plan showing the phasing of plan in annual and or five year
plans.
Planning Surveys Consists of following studies1. Economic Studies2. Financial Studies3. Traffic or Road use Studies4. Engineering Studies
2.1 Economic StudiesIt is important to find the service given by each road system to the population and products. Before estimation the requirement such that economic justification can be made details pertaining to the existing facilities should be available.The details to be collected include the following
1. Population and its distribution in each village town or other locality with the area classified in groups
2. Trend of population growth3. Agricultural and industrial products and their listing in classified groups, areawise.4. Industrial and Agricultural development and future trends5. Existing facility with regards to communication recreation and education 6. Per capita income
2.2 Financial StudiesThe financial studies are essential to study the various financial aspects like source of income and the manner in which funds for the project may be mobilized.
1. Source of income and estimated revenue from taxation on road transport2. Living Standard3. Resources at local level, toll taxes, vehicle registration and fines.4. Future trends in financial aspects.
2.3 Traffic or Road use StudiesAll the details of the existing traffic their volume and pattern of flow should be know before any improvement could be planned. Traffic surveys should be carried out in the whole area and on selected routes and locations in order to collect the following particulars.
1. Traffic volume in vehicles per day, annual average daily traffic, peak and design hourly traffic volume
2. Origin and Destination Studies3. Traffic flow patterns4. Mass transport facilities5. Accidents, their cost analysis and causes6. Future trend and growth in traffic volume and goods traffic, trend in traffic pattern.7. Growth of passenger trips and the trend in the choice of modes.
2.4 Engineering studiesAll details of the topography, soil and other problems such as drainage, construction and maintenance problems should be investigated before a scientific plan or programme is suggested. The studies include.
1. Topographic survey2. Soil Survey3. Location and classification of existing roads4. Estimation of possible developments in all aspects due to the proposed highway
development5. Road life Studies6. Special Problems in drainage, construction and maintenance of roads.
3.0 Interpretation of planning survey
1. To arrive at the road network, out of the several alternate possible system, which has maximum utility
2. To fix up priority of construction projects, so as to phase the road development plan of an area in different periods of time such as five year plan and annual plans
3. To assess the actual road use by studying the traffic flow patterns. This data may therefore show areas of congestion, which need immediate relief.
4. Based on the traffic type and intensity and performance of existing type of pavements and cross drainage structures, a new structure may be designed using the data and past experience
4.0 Preparation of Master Plan and its PhasingMaster plan is the final road development plan for the area under study which may be a block, taluk district, state or the whole country. Based on the surveys conducted and plans prepared different possible road networks and improvements of some of the existing roads are proposed.In each proposal the population and productivity of each locality, the traffic flow, topography and all other details, both existing and possible changes in future are kept in view
If some target of road length has been fixed for the country on the basis of area or population and production or both the same may be taken as a guide for deciding the total length of road system in each alternative proposal.The next step is to compare the various alternative proposals of road system in hand and to select the one which may be considered as best under the plan period.
4.1 Saturation systemIn this system the optimum road length is calculated for the area based on the concept of obtaining maximum utility per unit length of road. Hence this system is called saturation system or maximum utility system. The factors considered for obtaining the utility per unit length are.
1. Population served by the road network2. Productivity served by the road network
a. Agricultural productsb. Industrial production
4.2 Population unitsSince the are under consideration may consist of villages and towns with different population, it is required to group these into some convenient population ranges and to assign some reasonable values of utility units to each range of population served.A set of utility units will be assigned to different population ranges.
Population Range Utility unit<500 0.25501-1000 0.501001-2000 1.002001-5000 2.00
From the population data, the number of towns and villages with population range served by each road system us found and then converted into the utility units served by each road. Thus the total number of units based on population can be obtained from each road system proposed.
4.3 Productivity unitsThe total agriculture and industrial products served by each road system should be worked out. The productivity served may be assigned appropriate values of utility units per unit weight. For example one thousand tonnes of agricultural products may be considered equivalent to one unit. Similarly industrial products are also assigned suitable utility units per unit weight. However raw materials are usually given lower utility units when compared to the industrial products.
4.4 UtilityThe total utility of each road system is found by adding the population units and productivity units, the total units are divided by the total road length of each system to obtain the utility per unit length.
Each road system having different layout and length would show different values of utility per unit length. The proposal which gives maximum utility per unit length may be chosen as final layout with optimum road length.
4.5 Phasing of road programmeThe road network to be constructed and improved in the plan period is decided while finalising the master plan of the road development project. The plan period may be long term, like that of the 20 year road plan or of shorter period like five year plans. But whatever be the plan period, it is necessary to phase the road development programme from financial considerations. In other words, it is necessary to fix up the priorities for the construction of each link of the road network development programme to decide which link should be taken up and which one the next and so on .
Problems:1. For a particular are there are 4 alternative plan proposals P Q R and S With different
road length, the details of population and products served are given below. Workout the utility per unit length for each of the system and indicate which of the plans yield the max utility based on the saturation system
Since the utility units are not given in the problem, we have to assume convenient values of utility units for both population and productivity as shown below.
Productivity Unit
1000 1
Now we have to multiply these utility units with population and productivity
For example the utility unit assumed for a population range of 1001-2000 is 0.25, so for the proposal P no of towns and villages with population in the range of 1001-2000 are 160. So multiply 160 with utility unit 0.25 so the utility will be 160*0.25=40, similarly we have to do the calculations for all the proposals are population. Similarly the utility unit assumed for productivity is 1. So for the proposal P total agricultural and industrial products are 200 so utility will be 200*1=200.
Next step is to add these total population and productivity units: i.e.,
Total utility for
Population for the proposal P=160*0.25+80*0.50+30*1+6*2= 122 Productivity for the proposal P=200*1=200
Higher priority should be given for the higher value of utility/unit length unit.
ProposalTotal road length
Total Population utilityTotal Productivity utility
Total Utility
Utility/unit length Priority
P 300 160*0.25+80*0.50+30*1+6*2= 122
200*1=200
122+200=322 322/300=1.073 2
Q 400 200*0.25+90*0.50+60*1+8*2=171 270*1=270
171+270=441 441/400=1.103 1
R 500 240*0.25+110*0.50+70*1+10*2=2 315*1=31 205+315 520/500=1.040 3
Population range Utility unit1001-2000 0.252001-5000 0.55001-10000 1>10000 2
05 5 =520
S 550 248*0.25+112*0.50+73*1+12*2=215
335*1=335
215+335=550 550/550=1.00 4
2. For the following data of population units of 0.5, 1.0, 2.0 and 1.0 per 1000 tonnes, 500 tonnes and 100 tonnes of agricultural, raw materials and industrial products respectively. Find the priority of the following road system
3. Three road links A B and C are to be constructed during a five year plan period. Suggest the order or priority for phasing the road construction programme based on maximum utility approach. Assume utility units of 0.5,1 and 2 for the three population ranges and 1 per 1000/100 tonnes of agricultural and industrial products respectively.
Note: Procedure remains the same with the utility units for population
Similarly utility units are also given for agricultural and industrial materials
It is given that for every 1000 tonnes of agricultural products we have to take utility unit of 1
For proposal A agricultural products is 250, so utility will be = 250*1= 250
Note: keep in mind the productivity given in this problem is in 1000t
For every 100 tonnes of industrial products we have to take the utility unit of 1
Population range
Utility unit
<500 0.5501-1000 1.01001-2000 2
For proposal A industrial production is 20, so utility will be = (20*1000/100)*1=200
5.0 Third twenty year road development plan (1981-2001)
Third twenty year road development plan also called as Lucknow Road Plan. The silent features of the plan are as follows.
1. The future road development should be based on the revised classification of road system consisting of primary secondary and tertiary road systems as mentioned below.
a. Primary roadsi. Expressways
ii. National Highwaysb. Secondary roads
i. State Highwaysii. Major District Roads
c. Tertiary roadsi. Other District Roads
ii. Village Roads2. The road network should be developed so as to preserve the rural oriented economy
and to develop small towns with all the essential facilities. All the villages with population over 500 should be connected with all weather roads
3. The overall road density in the country should be increased to 82km/100sq km area by the year 2001. The corresponding values of planned road densities are 40 km/100 sq km for hill areas of altitude upto 2100 meters above MSL and 15 km/ 100 sq km for altitude above 2100 meters.
4. The national highway network should be expanded to form square grids of 100 km sides so that no part of the country is more than 50 km away from a NH.
5. The length of SH and MDR required in a state or region should be decided based on both areas and number of towns with population above 5000 in the state or region
6. Expressways should be constructed along major traffic corridors to provide fast travel.7. All the towns and villages with population over 1500 should be connected by major
district roads and the villages with population 1000- 1500 by Other district Roads. 8. Roads should be built in less industrialized areas to attract the growth of industries.9. Long term master plan for road development should be prepared at various levels, i.e.,
taluk, district, state and national levels.10. The existing roads should be improved by rectifying the defects in the road
geometrics: widening of the pavements, improveing the riding quality of the pavement surface and strengthening of the pavement structure to save vehicle operation cost and thus to conserve energy
11. There should be improvement in environmental quality and road safety.
12. Construction of roads should generate employment, ensuring growth of industries and agriculture
5.1 Calculation of road length as per 3rd twenty year road development plan
1. Length of National Highway=Total Area/502. Length of state highway= Total Area/25 or 62.5*number of towns- length of National
Highways3. Length of Major District Road= Total Area/12.5 or 90* number of towns4. Length of ODR or village roads= Density of Road Network* Total Area- Length of
NH - Length of SH- Length of MDR
Problem:1. The area of a certain district in India is 13,400 sq. km and there are 12 towns as per
1981 census. Determine the lengths of different categories of roads to be provided in the district by the year 2001.
Solution:1. Length of NH, Km=13400/50= 168 km2. Length of SH:
a. By Area, SH, Km= 13400/25=536b. By area and no of towns= 62.5*12-13400/50=482km
Adopt higher length of SH=536 Km3. Length of MDR, in the District
a. By area, MDR, Km= 13400/12.5= 1072 kmb. BY no of towns, MDR, KM= 90*12= 1080km
4. Total length of all categories of roads may be assumed to provide an overall density of road length equal to 82km per 100 sq km area by the year 2001.NH+SH+MDR+ODR+VR=13400*82/100=10988 kmLength of NH+SH+MDR= 268+536+1080= 1884 km
Therefore length of ODR+VR=10988-1884=9104km Primary system= 268km Secondary system consisting of SH and MDR= SH+MDR= 536+1080=
1616km Tertiary system= ODR+VR=9104 km Total length = 10,988 km
6.0 Forth twenty year road development plan1. Construction of 10,000km of expressways by the end of 2021.2. To provide connectivity to all habitations having population of 1000 and above3. It is also proposed to upgrade nearly 1.94 lakh km length of existing rural roads which
are identified as the through routes of the core network
4. Special provisions for funding through budgetary and other sources shall be required to continue with the objective of road connectivity to habitation.
5. Maintenance has to taken to the top of the priority list to sustain the assets created6. Intra village. Habitation roads, also should be considered with higher priority starting
with villages having more than 1000 population7. GIS based database management should be created for all the states in a phased
manner based on the feedback from the pilot project in rajastan and himachal Pradesh8. The planning data at the block/ district level should be updated every 3-5years and
maintained as geo-referenced data9. Engineering design and detailed project report must be the basis for implementation
of rural roads in India10. Low cost marginal and industrial waste materials may be promoted for rural road
construction11. The standard construction technology should be used for ensuring quality of
construction. However, wherever possible labour based construction methods also may be adopted to create employment to local people.
12. Many low cost technologies like soil stabilization is not used often due to lack of appropriate mechanical devices. Such short comings must be removed by appropriate development for machineries.
13. Routine and periodic maintenance should be planned and executed with due budgeting for the funds.
14. In all development of rural roads the environmental issues must be safeguarded.
7.0 National Highway Development Project
The National Highways Development Project is a project to upgrade, rehabilitate and widen major highways in India to a higher standard. The project was implemented in 1998 under the leadership of Atal Bihari Vajpayee. "National Highways" account for only about 2% of the total length of roads, but carry about 40% of the total traffic across the length and breadth of the country. This project is managed by the National Highways Authority of India (NHAI) under the Ministry of Road, Transport and Highways. The NHAI has implemented US$ 71 billion for this project, as of 2006.
Phase I: The Golden Quadrilateral (GQ; 5,846 km) connecting the four major cities of Delhi, Mumbai, Chennai and Kolkata. This project connecting four metro cities, would be 5,846 km (3,633 mi). Total cost of the project is Rs.300 billion (US$6.8 billion), funded largely by the government’s special petroleum product tax revenues and government borrowing. In January 2012, India announced the four lane GQ highway network as complete.
Phase II: North-South and East-West corridors comprising national highways connecting four extreme points of the country. The North-South and East-West Corridor (NS-EW; 7,300 km) connecting Srinagar in the north to Kanyakumari in the south, including spur from Salem to Kanyakumari (Via Coimbatore and Kochi) and Silchar in the east to Porbandar in the west. Total length of the network is 7,300 km (4,500 mi). As of April 2012, 84.26% of the project had been completed and 15.7% of the project work is currently at progress.[3] It also includes Port connectivity and other projects — 1,157 km (719 mi). The final completion date to February 28, 2009 at a cost of Rs.350 billion (US$8 billion), with funding similar to Phase I.
Phase III: The government recently approved NHDP-III to upgrade 12,109 km (7,524 mi)of national highways on a Build, Operate and Transfer (BOT) basis, which takes into account high-density traffic, connectivity of state capitals via NHDP Phase I and II, and connectivity to centres of economic importance. contracts have been awarded for a 2,075 km (1,289 mi).
Phase IV: The government is considering widening 20,000 km (12,000 mi) of highway that were not part of Phase I, II, or III. Phase IV will convert existing single
lane highways into two lanes with paved shoulders. The plan will soon be presented to the government for approval.
Phase V: As road traffic increases over time, a number of four lane highways will need to be upgraded/expanded to six lanes. The current plan calls for upgrade of about 5,000 km (3,100 mi) of four-lane roads, although the government has not yet identified the stretches.
Phase VI: The government is working on constructing expressways that would connect major commercial and industrial townships. It has already identified 400 km (250 mi) of Vadodara (earlier Baroda)-Mumbai section that would connect to the existing Vadodara (earlier Baroda)-Ahmedabad section. The World Bank is studying this project. The project will be funded on BOT basis. The 334 km (208 mi) Expressway between Chennai—Bangalore and 277 km (172 mi) Expressway between Kolkata—Dhanbad has been identified and feasibility study and DPR contract has been awarded by NHAI.
Phase VII: This phase calls for improvements to city road networks by adding ring roads to enable easier connectivity with national highways to important cities. In addition, improvements will be made to stretches of national highways that require additional flyovers and bypasses given population and housing growth along the highways and increasing traffic. The government has not yet identified a firm investment plan for this phase. The 19 km (12 mi) long Chennai Port—Maduravoyal Elevated Expressway is being executed under this phase.
8.0 Noteworthy Features of the PMGSY
The Ministry of Rural Development (MoRD) has been entrusted with the task of organising the programme. Some of the noteworthy features of the programme are:
Full Central funding, with 50% of the cess on High Speed Diesel being earmarked for this programme.
Preparation of Master Plans and Core Network for Rural Roads for all the Districts and Blocks, identifying the unconnected habitations and proposing the most cost-effective routes for the purpose.
Design and Specifications as contained in the Rural Roads Manual (RRM, IRC SP:20), published by the Indian Roads Congress (IRC).
Appointment of a dedicated State Level Agency in all States with overall responsibility for rural road planning, programme execution and management.
Appointment of programme implementing agencies, by all States, typically Public Works Departments (PWDs) or Rural Engineering Organisations (REOs).
Independent State Technical Agencies (STA) commissioned by MoRD to vet designs and estimates.
Use of competitive tendering by the implementing agencies of all works on the basis of a Standard Bidding Document (SBD).
Execution of the works within a period of 9-12 months. A Defects Liability and maintenance period of 5 years specified in the Contracts for
the roads constructed under the programme, with funds for maintenance being provided by the States.
A central on-line web-based financial and project monitoring system.
A 3-tier Quality Management System. Operational management at Central level by the National Rural Roads Development
Agency (NRRDA)
9.0 KSHIP
1. KSHIP play a fundamental role in the Government of Karnataka’s development strategy to sustain economic growth and regional development through infrastructure improvements
2. Working closely with iRAP to ensure that the planned rehabilitation works eliminate high risk sections of road where possible
3. With financial assistance from the World Bank, the Karnataka Government had, in the year 2000-01, launched the First Karnataka State Highways Improvement Project (KSHIP-I), and has improved about 2375 kms of State Highways at a cost of Rs. 2030 crore
4. KSHIP has submitted proposal for maintenance under a 5-year OPRMC Package System in respect of 1790.30 kms of State Highways that are not covered by the KRDCL maintenance package.
5. As per KSHIP laws, The drainage should always be clean with no stagnant water, and any water logging should be cleared within 24 hours.
a. Any broken pavement edge should be repaired within 7 days. b. Financial penalties have been prescribed for non-performance. c. The aim has been to make the arrangement as transparent as possible with a
view to minimise the chances of disputes.
10.0 KRDCL1. Mainly handles the maintenance aspects of the roads2. The Department has now come to believe that instead of the present input based road
maintenance contracting arrangement, it is advantageous to award long term road maintenance contracts and improve the quality of maintenance by providing performance specifications for the road.
3. The Department shall ensure quality control through independent monitoring, 4. The KRDCL packages had omitted the roads that were undertaken for improvement
under the KSHIP 5. The 3-year Maintenance Packages of the Karnataka Road Development Corporation
Ltd. (KRDCL) were determined 2-3 years ago and each package has a defined length of road and set scope of work.
6. Public Works Department (PWD) with officers of PWD, KSHIP and KRDCL to review and finalise the Bidding Documents for OPRMC in consonance with the guidelines made available by the World Bank in their Standard Bidding Document.
7. To have a separate establishment in place for the purpose of execution.
11.0 ROAD PATTERNS:
Road network can be laid in various patterns. These patterns in which the road network is laid could be1) Rectangular or Block pattern 2) Radial or Star and block Pattern
3) Radial or Star and Circular Pattern4) Radial or Star and Grid Pattern 5) Hexagonal Pattern6) Minimum Travel Pattern
1) Rectangular or Block pattern:
In this pattern, the whole area is divided into rectangular blocks of plots, with streets intersecting at right angles. The main road which passes through the center of the area should be sufficiently wide and other branch roads may be comparatively narrow. The main road is provided a direct approach to outside the city.
Advantages:
1) The rectangular plots may be further divided into small rectangular blocks for construction of buildings placed back to back, having roads on their front.
2) In this pattern has been adopted for the city roads. 3) The construction and maintenance of roads of this pattern is comparatively easier.
Limitations:
1) This pattern is not very much convenient because at the intersections, the vehicles face each other.
Example:
Chandigarth has rectangular pattern
2) Radial or Star and block Pattern:
In this pattern, the entire area is divided into a network of roads radiating from the business outwardly. In between radiating main roads, the built-up area may be planned with rectangular block.
Advantage:
1) Reduces level of congestion at the primary bottleneck location.2) If one is block then other side traffic can move.3) Vehicles face each other less than block pattern.
Limitations:
1) Proves particularly effective if two-lane ramp traffic does not have to merge at downstream end of ramp.
2) Safety appurtenances such as guide rail transitions, crash attenuators, and post support bases have not been designed to provide adequate protection at hazardous locations from the opposite direction of travel.
Example: Chandigarth has rectangular pattern
3) Radial or Star and Circular Pattern:
In this system, the main radial roads radiating from central business area are connected together with concentric roads. In these areas, boundary by adjacent radial roads and corresponding circular roads, the built-up area is planned with a curved block system. Advantages:
1) traditional intersections with stop signs or traffic signals, some of the most common types of crashes are right-angle, left-turn, and head-on collisions. These types of collisions can be severe because vehicles may be traveling through the intersection at high speeds. With circular pattern, these types of potentially serious crashes essentially are eliminated because vehicles travel in the same direction.
2) Installing circular pattern in place of traffic signals can also reduce the likelihood of rear-end crashes.
3) Removing the reason for drivers to speed up as they approach green lights and by reducing abrupt stops at red lights.
4) Because roundabouts improve the efficiency of traffic flow, they also reduce vehicle emissions and fuel consumption.
Limitations:
1) Centre lines of roads leading to circular pattern should be properly aligned with the central island.
2) Approach roads should be sufficiently curved, far enough in advance of circular pattern, to reduce vehicle speeds of entering drivers.
3) Islands separating the approach and exit lanes, known as splitter islands, should extend far enough to provide pedestrian refuge and to delineate the roundabout.
4) Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they are approaching a roundabout and that they should reduce their travel speed.
5) For older drivers declines in vision, hearing, and cognitive functions, as well as physical impairments, may affect some older adults' driving ability. Intersections can be especially challenging for older drivers.
4) Radial or Star and Grid Pattern : Change in direction, and because street patterns are the most enduring physical element of any layout, it could potentially contribute to systematic site planning and, consequently, deserves a closer look. Though the network is entirely interconnected, north-south movement becomes circuitous, indirect, and inconvenient, making driving an unlikely choice and vividly illustrating that interconnectedness by itself is insufficient to facilitate movement.
Advantages:
1) Keep vehicular traffic safe with a high proportion of 3-way intersections.2) Reduce cut-through traffic by similar or other means.3) Improve traffic flow in both directions.4) Improve land use efficiency and unit density.
Limitations:
1) Islands separating the approach and exit lanes, known as splitter islands, should extend far enough.
2) Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they should reduce their travel speed.
Examples: The Nagpur road plan formulae were prepared on the assumption of Grid pattern.
5) Hexagonal Pattern :
In this pattern, the entire area is provided with a network of roads formatting hexagonal figures. At each corner of the hexagon, three roads meet the built-up area boundary by the sides of the hexagons is further divided in suitable sizes.
Advantages:
1) Three roads meet the built-up area boundary by the sides of the hexagons.Limitations:
1) Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they should reduce their travel speed.
