Pages Menu
RssFacebook
Categories Menu

Widths & Buffers

This is a visual primer of how stuff fits… or doesn’t. It has been updated since its original publication with new dimensions in the 2012 AASHTO Guide.

Bicyclist Essential Operating Space

aashtoAccording to the 2012  AASHTO Guide for the Development of Bicycle Facilities, a bicyclist is 30″ wide, has an essential operating space of 48″ and a preferred operating space of 60″.

The 30″ width does not take into account many diverse human powered vehicles, such as trikes, utility bicycles, trailers and quadracycles. The guide has an illustration of other types of bicycles without detailed dimensions. The only one for which it indicates width is a child trailer—30″. (My utility trailer is 32″ wide.) There are no height dimensions for vehicles like recumbent trikes. Eye height is an important consideration in design, but never mind.

48″ of operating space is more consistent with a skilled bicyclist. A novice typically has more lateral travel than that. Since bicycle facilities are usually intended for novices, the 60″ preferred space should be the default consideration. But, of course, it won’t be, because bicyclists only get the minimum.

The 12ft lane

This illustration shows why a 12ft lane is not wide enough to share and is thus exempt from any FTR requirement. The lanes is too narrow to share and riding too far right compromises the bicyclist’s safety.

widths_squeeze-dually

American vehicles are wide! We don’t base our lane position on sharing the road with Mini Coopers and Smart cars. We’re anticipating SUVs, trucks and utility trailers. In 2006, the Ford F-Series was the best-selling passenger vehicle in the U.S. SUVs and trucks were the top-selling vehicle type until mid-2008. They are a significant percentage of the vehicles on the road.

Lane Control is Legal

widths_bmufl

When bicyclists use the full lane, most motorists change lanes. Passing clearance increases to 6-8ft and the bicyclist has plenty of space to avoid pavement hazards. She also has buffer space to her right in the rare event that a motorist tries to pass too close. Passing distance laws are irrelevant to cyclists who control their space. Which is a good thing, since they’re irrelevant to motorists when cyclists ride too far right.

The 14ft Lane

widths_14ft

Many state engineering guidelines use 14ft as a lane width that accommodates same-lane passing of bicyclists. On a road with trucks, buses, utility trailers or any other large, commercial vehicles, 14ft is NOT wide enough to share. It is not safe, therefor it is not PRACTICABLE.

The total outside width of any vehicle or its load shall not exceed 102 inches.
Lights, mirrors, or devices which are required may extend beyond the permissible width, no more than 10 inches on each side

Bike Lane FAIL

The following images are examples of typical shoe-horned bike lanes to show why the make things worse for bicyclists.

10-10-4

widths_10-10-4

A popular trend in recent years has been to divide a roadway with 24ft of width in each direction into what’s known as a 10-10-4. This is done to shoehorn minimal (4ft) bike lanes next to narrow (10ft) travel lanes. This helps no one. It scares the crap out of novices and takes away the right of informed bicyclists to ride in a safe and defensive manner. The trend needs to be killed.

Door Zone Bike Lanes

widths_dzbl-fdot

This drawing shows the measurements of Edgewater Drive. (except the parking spaces are only 7.5ft in many places). This is the FDOT standard for bike lanes next to parking (parking + BL = 13ft). Even though it exceeds the AASHTO minimum, there is barely enough space here for an open car door, a human body and a large vehicle to stand side by side, let alone operate with safe buffers). This bike lane design is unconscionable. It should be eliminated from all roads and design manuals.