The FHWA Small Town and Rural Multimodal Networks guide (STRMN) is the first and, as of July, 2018, the only federal guidance on ABLs (the STRMN refers to ABLs as Advisory Shoulders). The creation of STRMN used little information from countries more experienced with ABLs.

As a result, the STRMN fails to raise issues which other countries have encountered as problems and developed guidance to address.  Additionally, some of the guidance provided in the STRMN runs counter to guidance from more experienced countries. This may lead to ABLs in the US which are less safe or less comfortable than they could otherwise be.

This page captures those issues which I hope will be addressed either in future versions of ABL guidance or in future research efforts.

My knowledge is limited to two countries. First, the Netherlands, which originated the ABL concept, has used them for more than 40 years, and has over one thousand road-kilometers installed. Second, Denmark, which has been installing ABLs for more than 15 years and has more than 80 installed facilities. The perspective of other countries will be added as more work is finished. ​

Areas of Concern

  • Two Types of ABLs - Wide and Narrow
​Wide and Narrow 
  • High Vehicular Volumes
​There is no American data to support the FHWA's recommendation for a vehicular volume ceiling of 6,000 ADT.  2016 Dutch guidance recommends other solutions be found for roads over 4,000 ADT and sets an absolute maximum of 5,000 ADT. These higher volumes are only recommended on streets with lower speeds, i.e. 30 kph. Danish guidance recommends that ABLs not be placed on roads with more than 3,000 ADT.
A segment of a Minneapolis ABL peaks at 4,800 ADT so there is some evidence that higher volumes can work but how this one, short example applies to a wide range of streets and cities is unknown. 

  • Speed/Volume Tradeoff
STRMN provides two regions on the speed/volume graph illustrating conditions appropriate for ABLs. One region is labeled as "preferred" and includes all streets of 25 MPH and 3,000 ADT or less. The other region is labeled "potential" and includes streets with speeds from 25 MPH to 35 MPH and volumes from 3,000 ADT to 6,000 ADT.
Speed is a surrogate measure for the severity of a crash. Volume is a surrogate measure for the probability of a crash. Both measures are critically important to a user's perceived comfort in a facility.
To maintain a chosen level of safety or comfort, guidance should lower allowed volumes at higher speeds and vice versa. STRMN  
These regions do not recognize the speed/volume trade-off which XXXXXXXXXXx. 
. 
  • Center Lane Width
STRMN provides two regions on the speed/volume graph illustrating conditions appropriate for ABLs. One region is labeled as "preferred" and includes all streets of 25 MPH and 3,000 ADT or less. The other region is labeled "potential" and includes streets with speeds from 25 MPH to 35 MPH and volumes from 3,000 ADT to 6,000 ADT. 
  • Edge Lane Width
STRMN provides two regions on the speed/volume graph illustrating conditions appropriate for ABLs. One region is labeled as "preferred" and includes all streets of 25 MPH and 3,000 ADT or less. The other region is labeled "potential" and includes streets with speeds from 25 MPH to 35 MPH and volumes from 3,000 ADT to 6,000 ADT. 
  • Use of Color in the Edge Lanes
STRMN provides two regions on the speed/volume graph illustrating conditions appropriate for ABLs. One region is labeled as "preferred" and includes all streets of 25 MPH and 3,000 ADT or less. The other region is labeled "potential" and includes streets with speeds from 25 MPH to 35 MPH and volumes from 3,000 ADT to 6,000 ADT. 
Photos courtesy of Scott Robinson at City of Bloomington, IN