Interactive Highway Safety Design Model (IHSDM)

Interactive Highway Safety Design Model (IHSDM)

By Josh Hinds

The Modules

Outline

Background of IHSDM Description of the Modules New Features An IHSDM Project from Start to Finish Future Developments Conclusion

Background

What is IHSDM?

IHSDM is a suite of software analysis tools that evaluate the safety and operational effects of the geometric design on two-lane rural highways.

(www.ihsdm.org)

Background

What is IHSDM?

Safety analysis tool, not specifically used for designing.

Evaluates the geometric design of the highway.

Two-lane rural highways Compares user inputted design to

designated design standards.

The Modules

Why Was IHSDM Needed?

77% of the Nation’s highways are two-lane rural highways

41% of all the fatal crashes occur on two-lane rural highways

Citizens demand increased safety on two-lane rural highways

Background

Why Was IHSDM Needed?

The highway network is getting older.

Stakeholders are expecting safer highways on the same budget.

Highway designs need to be checked for safety ‘black spots’.

Background

How Does IHSDM Help?

Makes use of five software modules that analyze the geometric design of the highway– Policy Review– Crash Prediction– Design Consistency– Traffic Analysis– Intersection Review

Background

Framework of the IHSDM Program

IHSDM

Policy Review

Crash Prediction

Design Consistency

Traffic Analysis

Intersection Review(Coming Soon)

IHSDM is composed of these modules.

Background

How Does IHSDM Work?

The user inputs the design file. The five modules compare the inputted

design values to the AASHTO policy standard values.

IHSDM determines how far out of range the values are and provides feedback to the user.

Background

How Can IHSDM Benefit the Designer?

Intended to be used throughout the design process.

Can be used on new construction and existing facilities.

Provides a Quality Assurance check throughout the design process.

Background

How Can IHSDM Benefit the Designer?

Find ‘Accident Black Spots’ before construction.

Save money by lowering crash rates and eliminating the reconstruction of unsafe areas.

Double check design values. Uses design software format.

Background

How Can IHSDM Benefit the Designer?

Helps project developers improve the expected safety performance of the final design.

Justifies and defends geometric design decisions.

Background

How Can IHSDM Benefit the Designer?

- AASHTO A Policy on Geometric Design of Highways and Streets "Green Book"

- AASHTO Roadside Design Guide

- AASHTO Guide for Development of Bicycle Facilities

- Numerous Editions and Metric/English

Background

How Can IHSDM Benefit the Designer?

Public perception that the roadway is ‘safe’. Estimates the expected crash frequency for

the geometric design. Analyzes other safety and operation

performance measurements. (SSD, superelevation, etc.)

(Turner-Fairbank)

Background

What is ‘Safe’?

Every roadway will have crashes. ‘Safe’ (past)

– Meeting a minimum set of design criteria.

‘Safe’ (presently)– Comparison of number of crashes to sites with

similar characteristics.

(FHWA, Paniati)

The Modules

The Modules

FHWA was in charge of all the research FHWA received input from numerous state

agencies, consulting firms, and academic institutions.

Based on research received from field data.

The Modules

Policy Review Module

Automates the process of checking geometric design elements against relevant design policy standards.

Construction or Reconstruction

Quality Assurance / Quality Control

The Modules

Policy Review Module

Cross Section (traveled-way, auxillary, shoulder)

Horizontal and Vertical Alignment

Sight Distance Items with an asterisk

will be compared to FHWA standards.

The Modules

Policy Review Module

Summary of what will be analyzed

The Modules

Policy Review Module Results

The Modules

Crash Prediction Module

Identifies improvement projects on existing highways

Estimates the frequency and severity of crashes.

Compares the safety performance of design alternatives

Will assess that safety cost effectiveness of design decisions.

The Modules

Crash Prediction Module

Uses the Empirical Bayes Method Algorithm for estimating crashes combines base

models and accident modification factors Highway segments and intersections

– 3-leg stop control on the minor– 4-leg with stop control on the minor– 4-leg signalized

The Modules

The Modules

Crash Prediction Module

- The crash history

The Modules

Crash Prediction Module

Table– Crash Rate

By Design Element By Segment

– Crash Type

Graph– Expected Frequency– Crash Rate

By Design Element By Segment

The Modules

Crash Prediction Modulus

Module provides a comment section to inform the user of any areas not addressed.

Summary of what will be analyzed, and how the results are formatted.

Module runs analysis.

The Modules

Crash Prediction Modulus Results

Expected Crash Type Distribution

Crash Type Highway Segments Intersections Total

Single-vehicle accidents

  Collision with animal 16.6 (23.03%) 0.1 (0.08%) 16.6 (23.11%)

  Collision with bicycle 0.2 (0.22%) 0.2 (0.25%) 0.3 (0.48%)

  Collision with parked vehicle 0.4 (0.52%) 0.0 (0.03%) 0.4 (0.55%)

  Collision with pedestrian 0.3 (0.37%) 0.2 (0.33%) 0.5 (0.7%)

  Overturned 1.2 (1.71%) 0.1 (0.1%) 1.3 (1.82%)

  Ran off road 15.1 (20.94%) 0.3 (0.48%) 15.4 (21.43%)

  Other single-vehicle accident 1.9 (2.68%) 0.3 (0.41%) 2.2 (3.09%)

Total single-vehicle accidents 35.6 (49.49%) 1.2 (1.68%) 36.8 (51.17%)

Multiple-vehicle accidents

  Angle collision 2.1 (2.91%) 5.2 (7.26%) 7.3 (10.16%)

  Head-on collision 1.0 (1.42%) 0.3 (0.46%) 1.3 (1.87%)

  Left-turn collision 2.3 (3.13%) 1.6 (2.29%) 3.9 (5.42%)

  Right-turn collision 0.3 (0.45%) 0.1 (0.1%) 0.4 (0.55%)

  Rear-end collision 7.5 (10.36%) 6.6 (9.22%) 14.1 (19.58%)

  Sideswipe opposite-direction 1.3 (1.79%) 0.4 (0.51%) 1.7 (2.3%)

  Sideswipe same-direction 1.4 (1.94%) 1.0 (1.4%) 2.4 (3.34%)

  Other multiple-vehicle collision 2.2 (3.06%) 1.8 (2.55%) 4.0 (5.6%)

Total multiple-vehicle collisions 18.0 (25.04%) 17.1 (23.78%) 35.1 (48.83%)

Total accidents 53.6 (74.53%) 18.3 (25.47%) 71.9 (100.0%)

The Modules

Design Consistency Module

Provides a Quality Assurance check on the consistency of the design.

Allows designer to double-check design assumptions.

Some designs conform to policies, but can not be consistent for the drivers.

Heavily focused on Horizontal Curves.

The Modules

Design Consistency Module

Drivers are more likely to make mistakes at features that violate their human inclination.

Reduction of speed in tangent before horizontal curve.

Design speed vs. 85th percentile speed. Design conformance vs. driver’s expectations

The Modules

Design Consistency

Desired Speed = 85th percentile speed

62 mph was determined by studies in six states.

Tangent Speed

Design Speed Assumption Check (in the direction of decreasing stations)

StationV85 - Vdesign Speed

(mph) Condition

From To Min Max

14+281.693 11+157.303 6.2 12.0 2

11+157.303 10+986.321 0.0 6.2 1

10+986.321 9+771.386 (-7.1) 0.0 4

9+771.386 9+368.038 0.0 6.2 1

9+368.038 8+014.964 6.2 10.2 2

8+014.964 6+967.816 5.1 6.2 1

6+967.816 4+761.572 6.2 9.7 2

4+761.572 4+564.731 0.0 6.2 1

4+564.731 4+171.984 (-5.7) 0.0 4

4+171.984 3+703.461 0.0 6.2 1

3+703.461 349.458 6.2 12.0 2

349.458 0.000 4.3 6.2 1

Design Speed Assumption Check Conditions KeyCondition 1: 0 mph <= (V85 - Vdesign) <= 6 mphCondition 2: 6 mph < (V85 - Vdesign) <= 12 mphCondition 3: 12 mph < (V85 - Vdesign)Condition 4: (V85 - Vdesign) < 0 mph

where:V85 = estimated 85th percentile operating speed (mph)Vdesign = design speed (mph)

Speed Differential of Adjacent Design Elements Check (in the direction of increasing stations)

Station of max speed on

preceding element

Max speed on preceding element

(mph)

Start Station of curve

Speed on curve(mph)

Speed Differential(mph)

Condition

0.000 54.8 32.808 54.0 0.8 1

601.391 58.8 601.391 58.8 0.0 1

1+727.733 61.4 1+778.904 61.2 0.2 1

2+091.467 61.2 2+283.481 60.1 1.1 1

2+283.481 60.1 2+512.523 60.7 -0.6 1

3+015.503 61.5 3+301.391 59.3 2.2 1

3+301.391 59.3 3+703.461 60.0 -0.8 1

4+032.470 60.4 4+507.470 42.9 17.5 3

4+507.470 42.9 4+564.731 48.6 -5.7 1

4+788.698 50.1 4+788.698 50.1 0.0 1

4+788.698 50.1 5+708.100 55.8 -5.7 1

6+984.261 59.4 7+061.404 58.8 0.6 1

8+025.506 59.2 8+117.828 58.7 0.6 1

9+599.355 62.0 9+982.444 54.0 8.0 2

10+325.361 54.0 10+533.717 42.8 11.2 2

11+797.936 59.1 11+797.936 59.1 0.0 1

12+359.021 62.0 12+861.286 56.2 5.8 1

The Modules

Traffic Analysis Module

Evaluates the operational effects of the current and future traffic estimates.

Can be used to determine the effects of alternatives. (realignment, cross-section improvements, and additional passing lanes)

Construction or Reconstruction

The Modules

Traffic Analysis Module

Uses the TWOPAS rural traffic simulation model for two-lane highways.

QC/QA Provides documentation for design

exceptions Determines the time following other vehicles

The Modules

Traffic Analysis Module

Traffic Flow Traffic characteristics Highway Elements Time Parameters Results

Traffic Output Data / Main Section (16.404 to 14+116.404 increasing; 14+116.404 to 16.404 decreasing)

Traffic Output Data

Direction of Travel

Increasing Station

Decreasing Station Combined

Flow Rate from Simulation (v/hr) 299 303 602

Percent Time Spent Following (%) 39.6 44.9 42.3

Average Travel Speed (mph) 52.1 51.3 51.7

Trip Time (min/veh) 3.1 3.1 3.1

Traffic Delay (min/veh) 0.12 0.22 0.17

Geometric Delay (min/veh) 0.31 0.26 0.29

Total Delay (minutes/vehicle) 0.43 0.49 0.46

Number of Passes 0 0 0

Vehicle mi Traveled 797 808 1,605

Total Travel Time (veh-hrs) 15.3 15.7 31

The Modules

Traffic Analysis Module

TWOPAS– Traffic Simulation Model– User can specify traffic demand and vehicle mix.– Also, can specify horizontal and vertical

alignment.– Models 13 types of vehicles with performance

characteristics for each.

The Modules

Intersection Review Module

Not currently used in the 2006 edition. Research and module are complete. Still in the final testing phase. Expect the Intersection Review module to be

released very soon as an update to the 2006 edition.

The Modules

Intersection Review Module

Diagnostic review of the expected performance.

Uses the ‘Expert System’ Stopping Sight Distance Corner radius and turn lane design.

The Modules

The future of IHSDM

IHSDM is constantly being updated for the newest standards.

Research and data collection continues for all modules.

Additional modules are being researched and created. (intersection review)

Multi-Lane highways

The Modules

Conclusion