CE 552

- Typical crash rates and distributions- Crashes that take the highest toll on

human life

Rates …why?

• To compare locations• To decide if a location is at abnormal risk• Rate per million entering vehicles:

In-class calculation

In-class calculation

This should really be RHMVM, shouldn’t it?

Expected value analysis• Use only to compare “similar” sites (geometry, control, volume)

• Problem: crashes are non-neg. count data (normal distribution does not apply)

In-class calculation

Cluster analysis

• E.g., if a site has one right-angle, two rear-end and 6 left-turn crashes, one might say the left-turn crashes represent a cluster

• But … what if the # of left turns is very high … then, is 6 high?

• Need exposure data• Must usually use good engineering judgment

High Crash Location Methods

• Frequency• Rate • Severity/Cost• Some combination

– Iowa DOT uses .2F+.2R+.6C

• Critical Rate Factor method• Empirical Bayes

Critical Crash Rate Factor method

Error: this should say Z, not S

For derivation of equation and interpretation of terms, see link

Next step: engineering study at sites

Summarizing crash data

Type

EnvironmentalConditions a) light condition b) surface condition

Time Periodsa)Hourb)Dayc)Month

Severity, e.g., KABCO, MAIS

ContributingCircumstances

Typical crash ratesIowa data for risk by road typeOregon crash rates (compare to Iowa)

Guidelines for using NC crash ratesCrash rate discussion

Source: NCHRP Web Only Document 126

Aussie rates – compare road types

http://www.eurorap.org/library/pdfs/roaddesignfactors.pdf

Note: to convert /bvkm to /HMVM, multiply by ~6 (Iowa K+A+B crash rate per HMVM in ~60, much lower than the numbers presented above for Europe if you multiply them by 6)

Low traffic flow roads – there are significant differences in fatal andserious accident rate between roads with less than 10,000 AverageAnnual Daily Traffic (AADT), roads with 10,000 to 20,000 AADT, androads with more than 20,000 AADT. (The ratio of these differences isabout 2.3:1.8:1);

European crash rates by road type

Kentucky Intersection Crash Rates

http://www.ktc.uky.edu/Reports/KTC_03_21_SPR258_03_2I.pdf

Massachusetts Intersection Crash Rates

From Oregon Study …

http://www.oregon.gov/ODOT/HWY/TRAFFIC-ROADWAY/docs/pdf/safety_of_4-leg_vs_T.pdf

http://www.oregon.gov/ODOT/HWY/TRAFFIC-ROADWAY/docs/pdf/safety_of_4-leg_vs_T.pdf

http://www.oregon.gov/ODOT/HWY/TRAFFIC-ROADWAY/docs/pdf/safety_of_4-leg_vs_T.pdf

http://www.oregon.gov/ODOT/HWY/TRAFFIC-ROADWAY/docs/pdf/safety_of_4-leg_vs_T.pdf

Crashes that take the highest toll on human life

• Head-ons, Intersections, ROR, VRU• Show iRAP video

http://www.eurorap.org/library/pdfs/roaddesignfactors.pdf

Head-on collisions• head-on crash.• Fatal Head On Accident Six Killed On US12 Near Morton WA • Truck crossing median – 7 fatals video

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_500v20.pdf

Intersections (junctions)

http://onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_rpt_500v5.pdf

See: UMN captured crashes

Manner of collision

Run-off the road (ROR)

http://www.t2.unh.edu/nltapa/Pubs/fhwa's_roadway_departure_program.pdfhttp://www.t2.unh.edu/nltapa/Pubs/PLD-1.pdf

http://onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_rpt_500v6.pdf

http://www.t2.unh.edu/nltapa/Pubs/fhwa's_roadway_departure_program.pdf

Vulnerable Road usersMotorcycles, bikes, pedestrians

• Bicyclists and Other Cyclists (DOT-HS-810-986)• http://onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_rpt_500v10.pdf • http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_500v22.pdf

Children