11/03/11

Biking, Walking, & Blogging: New Tools coming to an engineer near you!Biking, Walking, & Blogging: New Tools coming to an engineer near you!

New Tools coming to an engineer near you!

From Tony Hull, BWTC

In October, TLC hosted a webinar, "Multimodal Level of Service in the 2010 Highway Capacity Manual" as part of the monthly webinar series by the Association of Pedestrian and Bicycle Professionals (APBP).  TLC/Bike Walk Twin Cities has now hosted 34 these webinars since February 2009 in an effort to provide educational opportunities to local transportation professionals. The APBP webinar series continues to bring relevant presentations on the latest practices by some of the leading professionals across the nation and October 2011 was no exception!

I know that it might be hard for some to get excited about new updates to the Highway Capacity Manual (HCM) and many probably think MMLOS (Multimodal Level of Service) is associated with candy consumption, but for the rest of us out in transportation geekdom this is a pretty big deal --especially those of us who are working to better integrate active transportation options around the Twin Cities.

Allow me to explain what all this means to the many of us not versed in the various technical manuals or their mystic acronyms. The first Highway Capacity Manual (HCM) was originally produced through a collaboration of the Transportation Research Board (TRB) and the Bureau of Highways (precursor to the FHWA - Federal Highway Administration) in 1950. The guide contained 147 pages in 8 volumes and provided a comprehensive toolbox of computations, concepts and guidelines for measuring the vehicle capacity and quality of service for Highways. 2010 is the 5th update to this manual. It now comes in a boxed set of 4 massive volumes, one an online resource that can be purchased directly from the TRB bookstore for just over $200.

The HCM has been used by transportation agencies for years as a tool for evaluating the needs and performance of our highway system. A quick note about highways: most of us think of highways as the large traffic moving arterials like freeways and state trunk highways, but the truth is the Manual on Uniform Traffic Control Devices (MUTCD) defines highway as a general term for the public traveled way including the entire area of the public right-of-way.

Essentially every street is a highway, although most of our local residential roadways operate at speeds and volumes that preclude the need for detailed computations of capacity and delay. But for our more significant roadways, the HCM provides tools and guidance to measure roadway performance and help prioritize the needs for roadway expansion.

The most commonly familiar performance measure is the Level of Service (LOS), which is a measure of vehicular capacity and delay intended to provide a consistent and objective measure that can be easily understood by transportation professionals, the public and decision makers. The fact is, the current level of service is consistent and objective (in terms of measuring needs for motor vehicles), but is easily misunderstood by the public, decision makers and even many transportation professionals. 

In most cases LOS is calculated for the AM and or PM peak hours to examine roadway or network capacity in terms of vehicle throughput and delay (congestion or gridlock) The measure is expressed in a seemingly intuitive letter grade system from A to F, as follows (from the AASHTO Policy of Geometric Design of Highways and Streets or "Green Book"):

Level of Service

A= Free flow
B=Reasonably free flow
C=Stable flow
D=Approaching unstable flow
E=Unstable flow
F=Forced or breakdown flow

Most of us can easily understand the relationship of the letter grade system and realize the E and F are not going to be acceptable, especially given our understanding of academic metrics where the F is synonymous with failure.  But unlike school grades, getting an A or a B is not usually the desired outcome.  In fact achieving LOS A or B for the peak period is likely an indication of wasted capacity, or underutilized roadway investments.  Sure if you are the motorist on the level of service A roadway, you will be pleased with the open road and uninterrupted travel to your destination, but as a tax payer, you may not be so pleased with the cost benefit of this equation.

With motor vehicle LOS the most desirable targets are to achieve C or D during peak hours, where the motorist may experience some delay or congestion, but the roadway is getting the most bang for the buck in terms of serving the most vehicles with the smallest footprint. Many agencies set targets of peak period LOS D for their networks and consider LOS E to be acceptable for short durations at selected locations.  This is why many of us become confused when transportation professionals present LOS in a public meeting about a project.  Most parents are not trying to raise D students and probably hesitate when being told they should support LOS D for streets in their communities. This confusion emphasizes the need for adding context when explaining LOS projections when informing the public and decision makers about roadway operations.

Additionally in the four previous versions of the HCM there were no reasonable measures for bicycling or walking and limited measures for transit (based mostly on roadway performance of buses and not about access for passengers).  In the 1985 and 2000 versions of the HCM, chapters were introduced providing considerations of bicycling and walking but without any tools or guidance to address the user needs in a meaningful way.  In fact, for decades there have been capacity/delay based measures and calculations for bicycles and pedestrians, but these follow the same principles of the vehicle LOS focused on available space and volume of users. Measures that are only useful in the highest volume pedestrian environments such as airports and sports arenas. Based upon the traditional pedestrian LOS measure, a six foot wide sidewalk directly adjacent to a six lane 45 mph highway would actually score an A or B based upon ample width of facility and lack of impedance from other pedestrian traffic, while at the same time a great pedestrian street like Nicollet Mall in downtown Minneapolis would very likely be an E or even F, based on the enormous amount of pedestrian traffic. 

Certainly the user needs and facility conditions for bicycling and walking are dramatically different than driving.  The new tools and calculations in the updated HCM are based on a wealth of new research that has mostly focused on quantifying the level of comfort and safety for walking and bicycling and less emphasis on congestion, which makes sense when you think about it.  The best streets for walking are full of people, but the ideal setting for driving is the empty open road.

The new MMLOS allows a project manager to input various attributes about the roadway and users into one model that then provides a LOS score for all modes in the corridor.  And unlike the Motor Vehicle LOS, achieving the highest letter grade for bicycling and walking actually is the best outcome possible based on the comfort and safety of users relative to the design of the facility and separation from moving traffic.  The new HCM does not provide a combined LOS for all modes, but rather allows for local jurisdictions to consider how best to prioritize roadway performance based upon trade-offs that can be examined by different design scenarios.

Consider the evaluation of transportation alternatives for a street based upon inclusion or exclusion of multimodal LOS.  A street reconstruction could involve the consideration of whether to add travel lanes to expand peak hour throughput or maintain a similar curb width and include medians, bicycle lanes and buffered sidewalks to address slower traffic and better accessibility for other roadway users.

With the old HCM, the quantitative analysis only provided for the movement of motor vehicles increasing the likelihood that a vehicle focused outcome is selected. 

OLD HCM vehicle only

Scenario 1: Added Lanes

Scenarion 2: Medians; bike lanes; buffered sidewalks

Vehicle LOS

B

D

 

The new HCM provides a snapshot of how each mode of transportation is impacted along the same roadway, allowing for a more meaningful consideration of the trade-offs.

NEW HCM multimodal

Scenario 1: Added Lanes

Scenarion 2: Medians; bike lanes; buffered sidewalks

Motor Vehicle LOS

B

D

Pedestrian LOS

E

B

Bicycle LOS

E

C

Transit LOS

D

C

 

Providing more robust information about how transportation design impacts each mode of travel allows for a more meaningful conversation about what solutions make the most sense.  The new multimodal LOS computations are a step toward a more Complete Street approach to our transportation network. So the next time you hear someone talking about level of service, be sure to confirm they are accounting for everyone in the computation.