Appendix C: UNC-Chapel Hill Bicycle Facility Design Approach

Bicycle Level of Service Example
Existing 6-Lane Arterial Street Retrofit with No Parking 3

Travel lane narrowing is recommended as the primary retrofit method to implement the planned network, with road widening (or median narrowing) reserved only for truly constrained situations where lane narrowing is not advisable or feasible. Nationally, narrowing lanes to add capacity to roadways is a relatively common practice for local and state transportation agencies. Lane narrowing to add vehicle capacity is widely accepted as a cost effective congestion mitigation strategy, but historically narrowing lanes to add bicycle facilities has not been as accepted. From a traffic safety standpoint, congestion creates a justification for adjusting lane widths to improve safety (by reducing crashes caused by congestion), which a majority of transportation officials feel comfortable pursuing as a mitigation strategy. However, when it comes to narrowing lanes to add bicycle lanes, agencies are typically concerned that narrowing lanes will reduce safety for motorists, reduce capacity or in some instances it is believed there is no demand for the bicycle facility to justify adjusting lane widths.

Providing additional width for the motorist has not proven to provide any safety benefit on low speed urban roadways. 4 Extra space provided to the parked vehicle and the bike lane reduces the potential for a hazardous crash between a bicyclist and an opening vehicle door and creates enough space where a bicyclist could pass another bicyclist without having to encroach into the adjacent travel lane. The resulting bicycle lane is more comfortable and is more likely to attract use.

The use of narrower travel lanes as a strategy for improving capacity and safety on urban arterials where posted speeds are 35 mph or lower is consistent with the 2011 AASHTO Green Book which states “lane width of 10 feet may be used in more constrained areas where truck and bus volumes are relatively low and speeds are less than 35 mph.” 5 This is backed up by recent research focused on the safety of travel lane widths varying between 10 and 12 feet for motorists operating on arterial roadways with posted speeds of 45 mph or less. 6 This research found lane width had no impact on safety or capacity under the majority of urban conditions. The study resulted in a virtual elimination of the capacity reduction formula in the 2010 HCM related to lane widths as it found little difference between 10, 11 and 12 foot lanes.

The AASHTO Green Book is vague with regard to defining what percentage of truck and bus volume is “low”, however there is guidance in research and pavement design guidelines that suggests 10% as a decision point.7 It should also be noted that wider lane widths may encourage motorist speeding. Adding bike lanes to these streets where there is sufficient right-of-way can reduce speeding and increase safety in residential neighborhoods and near schools. 8

3 The following assumptions apply to the roadway operating characteristics in this example: 6 travel lanes, 30,000 Average Daily Traffic, 45 mph, no parking occupancy, 2-foot gutter pan, good pavement (score 4.0 out of 5.0) and 50% directional split of traffic with 6% heavy vehicles. The gutter pan does not count in the measurement of available space in this situation.

4 Potts, Ingrid, Harwood, Douglas and Richard Karen, “Relationship of Lane Width to Safety for Urban and Suburban Arterials, TRB 2007 Annual Meeting

5 2011 AASHTO Green Book, Urban Arterial Travel Lane Widths, page 7-29

6 Potts, Ingrid, Harwood, Douglas and Richard Karen, “Relationship of Lane Width to Safety for Urban and Suburban Arterials, TRB 2007 Annual Meeting

7 TRB Special Report 214 – Designing Safer Roads, 1987. It is important to note this report documented research proving wider travel lanes increased safety, but this research was only based on rural, 2 lane highways.

8 Studies vary on the effectiveness of narrowing travel lanes as a speed reduction strategy. A majority of studies available for review generally find narrower lanes lower average speeds 3-5 mph, but a small number of studies have also found no change or slight increases in speeds.

The use of contrasting color was issued Interim Approval status by FHWA on April 15, 2011. The use of contrasting green color has been shown through experimentation to increase awareness of bicyclists but has so far not been shown to reduce crash rates in conflict areas. A written request must be submitted to the FHWA in order to implement green color pavement.

Design guidance and application from the interim approval for contrasting pavement state:

• The color green is designated as the color for bicycle facilities. The material used for green color can be paint, colored asphalt or concrete or other marking materials with the proper chromaticity and slip resistance.
• Green pavement marking may be used within a bicycle lane or within an extension of a bicycle lane to enhance the conspicuity of the lane or extension.
• If a pair of dotted lines is used to extend a bicycle lane across an intersection or driveway, or a ramp, green colored pavement may be installed between these lines as a supplement to the lines.

Bicycle Signal Head

Bicycle signals heads can provide more clear direction to bicyclists crossing signalized intersections that they may enter an intersection. This is particularly important at locations where bicyclists may be provided an advance or exclusive phase. At locations (typically trail crossings) where cyclists are expected to follow pedestrian signals, under present law and timing practices, bicyclists may only “legally” enter the crosswalk during the solid WALK portion of the signal, the walkway portion is significantly shorter than the provided walk plus clearance time. This often results in bicyclists disobeying the flashing DON’T WALK portion of the cycle which can lead to them being caught in the intersection during the change interval. Providing bicycle signals allows for a longer display of green as compared to the walk, which significantly improves the compliance with the traffic control. Further, the MUTCD states explicitly that pedestrian signals are for the “exclusive use of pedestrians”. Bicycle signals can be designed to call a green signal phase through the use of loop detectors (or other passive detection such as video or radar) or push button. Bicycle signal heads and a separate bicycle signal phase should be considered at intersections and trail crossings with very high volumes of cyclists or locations where it is desirable to provide separate phasing for the bicyclists.

The MUTCD has no provision for bicycle signals; however bicycle signals were issued interim approval for use by FHWA in December 2013. The NCUTCD has developed draft language for inclusion into an interim approval for FHWA’s consideration.

Rectangular Rapid Flashing Beacons

The use of RRFB was issued Interim Approval status by FHWA on July 16, 2008 for the use at pedestrian crossings. Research has shown higher motorist yielding rates for RRFB versus standard flashing beacons. A written request must be submitted to the FHWA to participate in the Interim Approval. A written request to experiment with the device would be required for use at locations intended primarily for bicyclists.

Pedestrian Hybrid Beacons (a.k.a: HAWK Signal – High Intensity Activated Crosswalk)

Signal Timing and Bicycle Detection

It was observed that the majority of collector and local street crossings of arterials at UNC-CH required actuation. The Town updated all signalized locations to detect bicyclists and marked the sweet spot for bicyclists detection with the bike detection pavement marking. Based on email discussions with staff, the minimum green time provided for crossing arterials is typically 5-6 seconds with extension time provided as motor vehicles are detected. Yellow and red times totaling 4-6 seconds are provided at each location to allow a motor vehicle to clear the intersection. Should a bicyclist attempt to cross one of the town’s 7 lane arterials (approximately 90 feet), they may not clear the intersection within the time provided. Section 9D.02 of the 2009 MUTCD states: “On bikeways, signal timing and actuation shall be reviewed and adjusted to consider the needs of bicyclists.” Accommodating bicyclists at actuated intersections is one relatively cost-effective way in which a town can make significant strides to improve the safety and level of service provided to bicyclists.

• Timings at signalized intersections should be modified on a case-by-case basis to consider the specific needs of bicycles, which have slower acceleration and operating speeds than motor vehicles. A stationary, or “standing”, cyclist entering the intersection at the beginning of the green indication and a moving, or “rolling”, bicyclist approaching the intersection towards the end of the phase should be considered. The needs of standing cyclists can typically be accommodated by increasing the minimum green time on an approach, which is the current state of the practice. The needs of rolling cyclists require increases to the yellow and red times (change and clearance intervals), which may result in a slight loss of capacity at the intersection.
• The minimum green time should be adjusted such that the total phase duration (minimum green time plus yellow and all red times) is long enough for a bicyclist leaving the stop bar at the beginning of the green indication to clear the far side of the intersection. This time is referred to as the Bicycle Standing Time and is sufficient for a bicyclist to react, accelerate and cross the roadway before the conflicting crossing traffic receives a green indication.
• At intersections with arterial roads and a side street of lower classification, there may be concern about the impact to delay on the arterial when the side street minimum green time is increased (i.e. by 4 seconds as the worst case scenario) to accommodate the bicycle standing time. However, the changes to the minimum green time should have a little, if any, impact to the delay for motor vehicles on the arterial. During peak periods, the green time allocated for a minor approach typically increases over the minimum green time due to high demand on the minor street. During off peak periods, the loss of green time allocated to an arterial road will have little impact due to the lower traffic volumes on the arterial.
• Change and clearance intervals (i.e. yellow and red times) provided for motor vehicles may sometimes be sufficient for bicyclists. Generally, the yellow times used for motorists, typically between 3 and 6 seconds, are suitable for cyclists. However, it may be necessary to consider lengthening the red time depending upon posted speed limit, intersection width, bicyclist speed, roadway grade and red time used for motorists. The difference in clearance time between faster motorists and slower bicyclists is exaggerated by increased crossing distances and increased motorists speeds; therefore, it is more challenging to accommodate bicycles in the signal timing at wide, high-speed intersections. Bicyclists traveling uphill may have even slower speeds than typical, further increasing their crossing times and requiring longer change and clearance intervals. As indicated above, increasing red times may be challenging due to potential decreases in motor vehicle capacity, increases in red-light running and increases in motor vehicle crashes. If it is determined that increasing the change and clearance interval are not feasible, it is recommended bicycle signal heads be evaluated to stop bicyclists from entering the intersection prior to the onset of the yellow indication which would be intended for motorists.

* Distance from Stop bar to far side of conflicting travel lane
**Assumes a 6 foot bicycle length and 10 mph operating speeds. Slower or faster operating speeds should be considered depending upon conditions (e.g. type of user, grade of road) at the intersection.

Crossing Islands

Crossing islands facilitate crossings of multiple lane and/or high-volume arterials by providing space in the center of the roadway. They allow the pedestrian or bicyclist to focus on one direction of traffic at a time (two-stage crossing). Median islands (or crossing islands) are constructed at the center of a road to physically separate the directional flow of traffic and to provide pedestrians and bicyclists with a place of refuge while reducing the crossing distance between safety points.

Arterial roadway intersections that have low demand for left-turn movements can be potential candidates for adding median islands. Median islands can be constructed on these roadways by using the available center turn lane area or by removing parking from one side of the street and shifting the travel lanes. Median islands are likely to be a medium- or long-term improvement on roadways where significant channelization changes are needed to provide enough space for the median island

The newest AASHTO Guide outlines design considerations for median crossing islands:

• Median islands are beneficial to install on roadways that have high traffic volumes, roadways that are too wide for full roadway crossing and roadways with more than three travel lanes.
• Minimum width for storage on the median is 6 feet. 10 feet accommodates a bike with trailer.
• Island should be large enough for multiple people to be on the island at once (e.g. strollers, bicyclists and pedestrians etc.)
• Angling the refuge area at approximately 45 degrees is recommended to direct those crossing to face towards on-coming traffic.

Advanced Yield Markings

Advanced yield markings in conjunction with “YIELD HERE TO PEDESTRIANS” signs have proven to be effective at reducing multiple threat crashes at uncontrolled, marked crosswalk locations. A multiple threat crash results when a car in one lane stops to let the pedestrian cross, blocking the sight lines of the vehicle in the other lane of a multi-lane approach which advances through the crosswalk and hits the crossing pedestrian(s). The MUTCD (2009) requires the use of “YIELD HERE TO PEDESTRIANS” (R1-5, R1-5a) signs if yield lines (shark’s teeth) are used in advance of a marked crosswalk that crosses an uncontrolled multi-lane approach. “YIELD HERE TO PEDESTRIANS” signs may also be used without the installation of advanced yield lines. If yield lines and “YIELD HERE TO PEDESTRIANS” signs are used in advance of a crosswalk, they should be placed together and 20 to 50 feet before the nearest crosswalk line; parking should be prohibited in the area between the yield line and the crosswalk. “YIELD HERE TO PEDESTRIANS” signs may be used in conjunction with the “PEDESTRIAN CROSSING” (W11-2) warning sign but must be on a preceding post and not block the road user’s view of the W11-2 sign. This application should be considered at trail crossings, pedestrian hybrid beacon crossings and bicycle boulevard crossings of arterials. It is recommended the bicycle symbol be incorporated onto the signs. If a pedestrian hybrid beacon is used at a crossing location, then a “CROSSWALK STOP ON RED” (R10-23) should be used per Section 2B.53 of the MUTCD.

High-visibility Pedestrian/Bicycle Crossing Warning Signs

High-visibility bicycle and pedestrian warning signs are recommended at trail crossings. These signs can increase driver awareness of bicyclists and pedestrians, especially at mid-block locations where bicyclists and pedestrians may not be expected. These signs will be most effective when combined with other treatments, such as marked crosswalks, curb extensions and median islands, etc. Signs should be used judiciously—too many signs can cause visual clutter and lead to non compliance. High visibility bicycle and pedestrian signs are incorporated into the new MUTCD.

Crossings at Off-Set Intersections

Greater detail on all of these design treatments can be found in the documents mentioned above, as well as other sources such as PedSafe11 and the NACTO website.

10 AASHTO Guide for the Development of Bicycle Facilities