RURAL HIGHWAY SHOULDERS THAT ACCOMMODATE BICYCLE AND PEDESTRIAN USE (TxDOT Project 0-6840) June 7, 2016 Presented by: Karen Dixon, Ph.D., P.E., TTI Team: Kay Fitzpatrick, Raul Avelar, & Subasish Das
Project Objectives Define roadway shoulder suitability criteria for pedestrians and bicycles Apply criteria to Texas highways to determine candidate locations that merit shoulder improvements Identify high use or high demand locations Develop a list of target locations, coupled with the suitability criteria 2
Outline of Presentation Background Data Collection Analysis Recommendations Questions / Discussion 3
Background: Literature Review / State of Practice 4
Application Best Use Width Motor Vehicle Design Speed Traffic Volume Classification or Intended Use Other Considerations General Considerations for Paved Shoulder Use by Bicycles Paved shoulders Rural highways connecting town centers and other major attractors. Based on road s context and conditions in adjacent lane: 4-ft width is a minimum value (typical), 5-ft widths generally recommended. Additional width when motor vehicle speeds > 50 mph. Variable. Typical 40 55 mph. Variable. Rural roadways; inter-city highways. Provides more shoulder width for roadway stability. Consider characteristics of the adjacent motor vehicle traffic, (i.e., wider shoulders on higher-speed and/or high-volume roads). Source: Based on Table 2-3, pp. 2-17 to 2-20 in the Guide for the Development of Bicycle Facilities (AASHTO, 2012) and Multiple State Guideline Documents 5
Most Common Considerations for Shoulder Width Selection Traffic Operations (volume, speed, vehicle type, facility type) Connectivity Land Use Vertical Grade (> 5%) Presence and configuration of rumble strips 6
Current Texas Shoulder Width Requirements (1 of 3) Existing Suitability Criteria and Considerations Existing Suitability Criteria Supporting Data Shoulder Width: 4 ft min. if speed limit is >35 mph (5 ft at rural locations with ADT > 400 vpd and where bridge decks are being replaced) Paved Shoulder Speed Limit Functional Classification Traffic Volume Number of Lanes 7
Current Texas Shoulder Width Requirements (2 of 3) TxDOT Shoulder Widths for Rural Two-Lane Highways Functional Class Design Speed (mph) Minimum Width (ft) for ADT of < 400 400 1500 1500 2000 > 2000 Arterial All 4 a 4 or 8 a 8 a 8 10 a Collector All 2 b,c 4 c 8 c 8 10 c Local All 2 4 4 8 a On arterials, shoulders fully surfaced. b On collectors, use minimum 4-ft shoulder width at locations where roadside barrier is used. c For collectors, shoulders fully surfaced for 1500 or more ADT. Shoulder surfacing not required but desirable even if partial width for collectors with lower volumes and all local roads. Source: Based on Table 3-8, p. 3-27 TxDOT (2014). 8
Current Texas Shoulder Width Requirements (3 of 3) TxDOT Shoulder Width Requirements for Multilane Highways Type of Facility Shoulder Width (ft) Four-Lane Undivided Four-Lane Divided Six-Lane Divided 8 a to 10 8 a to 10 8 a to 10 a Applies to collector roads only. On four-lane undivided highways, outside surfaced shoulder width may be decreased to 4 ft where flat (1V:10H), sodded front slopes are provided for a minimum distance of 4 ft from the shoulder edge. Source: TxDOT (2014) 9
Overview of Data Collected/Acquired for Analysis 10
Summary of Data Roadway Inventory Data (RHiNo) Crash Data for Pedestrian and Bicycle Involved Crashes (CRIS) US Census Data (Household Information) National Households Travel Survey Data (Bicycle and Pedestrian Trips) Sample Data for Shoulder Conditions (Video Data for Two Districts) Field Observational Data 11
Key Study Corridors Rural two-lane roadways Rural multilane roadways 12
Inspecting the Data 13
Rural Two-Lane Highways Slope Graph Showing Differences in Bicycle and Pedestrian Injury Types 14
Rural Two-Lane Highways Distribution of Factors Factor Roadway Alignment Surface Condition Lighting Condition Weather Condition Category Shoulder Width 5' (Percent) Shoulder Width > 5' (Percent) Curve 9.3 7.4 Straight 90.7 92.7 Dry 95.4 92.7 Wet 4.7 7.4 Dark 55.8 63.7 Day 44.2 36.3 Clear 86.1 81.9 Cloudy 10.5 12.8 Rain 3.5 5.4 Typical Bicycle/Pedestrian crash occurred at tangent locations, with dry surface conditions, during dark conditions on clear days. 15
Rural Multilane Highways Slope Graph Showing Differences in Bicycle/Pedestrian Injury Types 16
Rural Multilane Highways Distribution of Factors Factor Roadway Alignment Surface Condition Lighting Condition Weather Condition Category Shoulder Width 5' (Percent) Shoulder Width > 5' (Percent) Curve 0.0 3.5 Straight 100.0 96.6 Dry 85.7 89.7 Wet 14.3 10.4 Dark 57.1 55.2 Day 42.9 44.8 Clear 85.7 82.8 Cloudy 0.0 13.8 Rain 14.3 3.5 17
Descriptive Statistics Factors Statistics Rural Two-Lane Rural Multilane Annual Average Minimum 404 2814 Daily Traffic Mean (Average) 5448 11,767 (vpd) Maximum 23,416 29,957 Speed Limit (mph) Shoulder Width (ft) Minimum 40 40 Mean (Average) 59.78 61.53 Maximum 75 75 Minimum 1.0 1.0 Mean (Average) 6.6 6.8 Maximum 10.0 10.0 18
Analysis and Findings 19
Probability (Statistical) Findings As the speed limit increases and shoulder widths remain constant, crashes involving bicycles and pedestrians can be expected to increase. As shoulder widths are increased and speed limits are held constant, crashes involving bicycles and pedestrians can be expected to decrease. 20
Quantitative Effects for Rural Two- Lane Highways For each 5 mph increase in speed limit, the shoulder width should be increased by approximately 1.68 ft to offset safety issues introduced from the increased speed limit. 21
Mosaic Plot for Rural Two-Lane Shoulder 22
Mosaic Plot for Rural Two-Lane Speed Limit 23
Quantitative Effects for Rural Multilane Highways For each 5 mph increase in speed limit, the shoulder width should be increased by approximately 1.0 ft to offset safety issues introduced from the increased speed limit. 24
Mosaic Plot for Rural Multilane Shoulder 25
Mosaic Plot for Rural Multilane Speed Limit 26
Determining Bicycle/Pedestrian Demand Conducted an analysis using land use and household information from the US Census Supplemented Census data with information from the National Households Travel Survey Based on the following explanatory variables: Population density per square mile Housing units per square mile Percent renter-occupants Household size (number of people per household) 27
Estimating Demand for Rural Bicycle and Pedestrian Trips 28
Field Observation Findings Individual bicyclists rarely travel along rural corridors with very narrow shoulders Bicycle groups do use these facilities but often take the entire lane When a vehicle does pass a bicycle, the cyclist tends to shift to the right and the vehicle to the left (as expected) Sample size too small to use for any computational analysis 29
Sampling of Shoulders for Suitability Sampled rural roads in the TxDOT Districts of Houston (1947 roadway segments) and San Antonio (4294 roadway segments) Identified rumble strips and shoulder widths using RHiNo and Google tools Determined application of rumble strips varied substantially between Districts and should be assessed on a case-by-case basis 30
General Conclusions Shoulders must be paved, well maintained, and of a type that facilitates use by bicycles or pedestrians. Locations where longitudinal rumble strips are present should allow additional lateral separation on the shoulder and the rumble strips should provide spaces to permit bicycles to safely enter and exit the shoulder region. As the risk to non-motorized users increases due to high speeds or volumes, the shoulder widths should increase to accommodate additional space. 31
Recommended Shoulder Widths at Locations with Bicycle and Pedestrian Activity Facility Rural Two-Lane Highway (1.68' shoulder width increase for each 5 mph increase) Rural Multilane Highway (1.00' shoulder width increase for each 5 mph increase) Speed Limit (mph) Calculated Shoulder Width No Rumble Strips (ft) Rounded Shoulder Width No Rumble Strips (ft) 55 6* 6 Shoulder Width for Locations with Rumble Strips (ft) 60 6 + 1.68 = 7.68 8 Add at least 1 65 6 + 2(1.68) = 9.36 10 70 6 + 3(1.68) = 11.04 11 55 8 (minimum)* 8 9 60 8 + 1.00 = 9.00 9 10 65 8 + 2(1.00) = 10.00 10 10 to 11** 70 8 + 3(1.00) = 11.00 10 to 11** 10 to 12** * Based on TxDOT (2014), Table 3-8, p. 3-27 and companion content ** A range of shoulder widths is presented because shoulders wider that 10 ft often will be used by motor vehicles as secondary lanes (particularly at intersection locations) and create additional problems 32
Recommended Shoulder Suitability Criteria Description Shoulder Width (No Rumble Strips Present) (ft) Shoulder Width (Rumble Strips Present and/or Vertical Grades 5%) (ft) Speed Limit (mph) Rural Two-Lane Roadway* Rural Multilane Roadway* 55 6 8 60 8 9 65 10 10 70 10 to 11** 10 to 11** 55 9 May add 1' at 60 10 locations with these 65 10 to 11** features** 70 10 to 12** Adjacent Motor Vehicle Travel Lane (ft) All 11 to 12 11 to 12 Rumble Strip Configuration All Where present, rumble strips should have 12' periodic gaps at intervals of 40 to 60' Shoulder Surface Type and Quality All Fully paved with surface similar to that of adjacent motor vehicle lane Pavement Maintenance All Routine maintenance required to maintain debris free riding surface *Add an additional 1' shoulder width at locations where roadside obstacles such as guardrails or barrier are present. ** A range of shoulder widths is presented because shoulders wider that 10 ft often will be used by motor vehicles as secondary lanes (particularly at intersection locations) and create additional problems 33
Procedure to Prioritize Shoulder Widening (1 or 2) Step 1: Select type of road and study area. Determine the household population density or future expected land use density to use for predicting the number of nonmotorized trips (by using the graphic shown in Figure 19). Step 2: Determine the lane and shoulder width and shoulder pavement type. Step 3: Narrow down the list of candidate corridors to those with paved shoulder widths that are less than the recommended widths. Note that rumble strip and barrier information may not be known at this stage. 34
Procedure to Prioritize Shoulder Widening (2 or 2) Step 4: Sort the corridors identified in Step 3 based on total number of non-motorized trips. Step 5: Examine and prioritize the remaining corridors by performing an examination of the individual locations to determine conditions including rumble strips, guardrail or barrier, and steep vertical grades. Also, examine locations with gaps where shoulders do not meet the criteria for sections of the road. This connectivity evaluation should focus on short connections between communities of up to 3 miles. Step 6: Rank the resulting corridors. 35
Questions? Discussion? 36
Extra Slide Strategic Corridor Development Plan Introduces the ranking procedure including the trip estimation calculation and the recommended suitability criteria Provides ranked list of two-lane highway sites (28 locations) Provides ranked list of multilane highway sites (13 locations) Includes maps for individual districts 37