Roadway Safety For Local Agencies

Doug BishTraffic Services Engineer

Oregon Department of Transportation

Roadway Safety For Local Agencies

Safety at ODOT

• What is SPIS anyway?

• What does SPIS mean?

• Why is it important?

• A little about Discretionary Immunity

Roadway Safety For Local Agencies

SPIS (Network Screening)

• SPIS is just a model, one way to prioritize

“All models are wrong, but some are useful”

• Crash histories are subject to random variations, one year will be high the next low.

“Just wait a year and this intersection will improve”

Roadway Safety For Local Agencies

SPIS (Network Screening)

A Data Driven Process:• Safety Priority Index System (SPIS)

– Oregon DOT’s primary tool for selecting and identifying problem locations since 1986

– Uses 3 years of crash data– Uses a tenth of a mile “sliding” window– Use of multiple measures overcomes

weaknesses of any one– Still not perfect, does not account for RTM *RTM (regression to the mean) do anything today to a high crash site and it will look

like it improved next year (i.e., natural variation looks like real change)

Roadway Safety For Local Agencies

SPIS Sliding Window• Each “window” slides a hundredth of a mile and recalculates SPIS for another tenth of a mile.

• Eligible for SPIS if there is either one fatal or 3crashes of any severity

Tenth of a mile “windows”

FatalInjury A

Injury B PDO

1st segment – 1 F and 1 A (one fatal – SPIS eligible)2nd segment – 1 F and 1 A (one fatal – SPIS eligible)

3rd segment – 1A, 1 B, and 1 PDO (3 crashes, SPIS eligible)4th segment – 1 B and 1 PDO (2 crashes, not SPIS eligible)

RoadwayPDO

Roadway Safety For Local Agencies

SPIS (Network Screening)

SPIS is similar to a “black spot” map used to prioritize high crash locations, but combines the best of different indicators—

• Crash Rate has tendency to over-emphasize low volume roads with a few crashes

• Crash Frequency has a tendency to over-emphasize higher volume roads with many crashes

SPIS combines Frequency, Rate and Severityinto one index.

Roadway Safety For Local Agencies

SPIS (Network Screening)

SPIS = Frequency + Rate + Severity (using 3 years of Crash data to generate a composite index)

• Crash Frequency (25%)– 150 crashes in a tenth of a mile produces a maximum score of 25

• Crash Rate (25%) – 7 crashes per mvm produces a maximum score of 25

• Crash Severity Ranking (50%) – Fatal and Injury A crashes 100 points each– Injury B and C crashes 10 points each– PDO crashes 1 point each– 300 points produces a maximum score of 50

Roadway Safety For Local Agencies

Example of SPIS

SPIS

0 Fatal accidents 14,200 ADT

1 Inj. A accidents

0 Inj. B accidents 10.95 Frequency portion

3 Inj. C accidents 4.99 Rate portion

4 PDO accidents 22.33 Severity portion

8 Total accidents   38.27 SPIS value

SPIS

1 Fatal accidents 20,000 ADT

2 Inj. A accidents

4 Inj. B accidents 15.17 Frequency portion

5 Inj. C accidents 7.80 Rate portion

8 PDO accidents 50.00 Severity portion

20 Total accidents   72.97 SPIS value

Severity will reach maximum score of 50 with 3 F&A or 2 F&A and 10 B&C.Frequency will reach a score of 20 at about 50 crashes, and a maximum score of 25 at 150 crashes.Rate is dependent on the ADT and will reach maximum score of 25 at a rate of 7 crashes per mvm.

Top 5% SPIS Example Top 15% SPIS Example(about 54 and above) (about 37 to 44)

Roadway Safety For Local Agencies

SPIS (Network Screening)

• The result is a list of sites ordered according to score.

• The sites with the highest score may or may not be those most likely to benefit from measures to reduce crashes.

• Sites must be investigated to determine if they are good sites for fixing.

• Not all sites in the top have cost effective fixes.• Trying to find sites with “most bang for the buck”.

Roadway Safety For Local Agencies

SPIS Maps and Reports

Roadway Safety For Local Agencies

SPIS for All Public Roads (future)

• ODOT is working on a new version of SPIS for all public roads

• Based on GIS

• Flexible, can be adjusted for each jurisdictions needs

• Will produce a SPIS ranking for all public roads

Roadway Safety For Local Agencies

Why is something like SPIS important?

• To identify and rank sites most likely to benefit from a crash reduction countermeasure

• Helps to prioritize safety on the system

• Helps to consider safety in decision making

• A priority system like SPIS can help with discretionary immunity

Roadway Safety For Local Agencies

What is Discretionary Immunity?Discretionary immunity means that the jurisdiction (or it’s

employees) cannot be held liable for discretionary decisions (i.e. how your agency is going to prioritize your safety spending).

A discretionary decision is a policy level decision that involves a balancing of social, political, economic, and safety considerations.

Discretionary immunity applies when the plans and policies were adopted at the highest levels.

Discretionary immunity helps assure that decisions on how best to use limited resources can and will be made (not by fear of the courts).

Roadway Safety For Local Agencies

What is Discretionary Immunity?

An example:

The state is sued because they failed to put a traffic signal in at a crosswalk and a child was hit in the crosswalk.

• The state has limited funds for safety improvements (as set by the Commission)

• Documented safety program - spending and priorities• Use the funds to improve the highest priority sites• Could be demonstrated this crosswalk was a lower priority

with a tool like SPIS

Roadway Safety For Local Agencies

How can a good safety program protect You?

• Prioritizing safety decisions by a well thought out process.• Set aside some funds specifically for Safety improvements.• Making decisions about spending safety dollars based on

documented process.• Documenting the decisions (document, document,

document!). • Policy decided at the highest policy setting level (get your

council or commission to approve and support the program).

• Check with legal counsel about discretionary immunity.

Roadway Safety For Local Agencies

How can a good safety program protect You?

• If we identify it and don’t fix it aren’t we in trouble?

No as long as you are following your policy as set by higher levels. “You have limited funds and can’t fix everything”.

• If we don’t know about we aren’t liable, right?

Wrong, you can be held liable regardless, especially if you should have known about it or if someone had informed you of it (i.e., “the public complained several times about the intersection”).

Roadway Safety For Local Agencies

Questions?

Doug Bish

Traffic Services Engineer

Oregon Department of Transportation