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The "Bicycle Compatibility Index" - critique of implementation manual and workbook
John S. Allen
The University of North Carolina Highway Safety Research Center has conducted research leading to publication by the Federal Highway Administration (USA) of an implementation manual for a so-called "Bicycle Compatibility Index" ("BCI"). This critique addresses mainly the implementation manual.
Really only a comfort index, and less than satisfactory as one
Level of service as conventionally defined describes traffic flow: unimpeded, congested, gridlocked. In a modern GIS database containing traffic data, an area-wide evaluation can be carried out automatically once the parameters of a formula are included in the database software. However, the BCI does not meet the requirement for such analysis, for several reasons.
Effect of linear model on the contribution of motorist speed
Increased speed of motorists' overtaking bicyclists may adversely affect the bicyclists' comfort and safety, but has little effect on bicyclists' mobility except as it affects their making left turns. On the other hand, when motorists are stopped or traveling slower than bicyclists, bicyclists' mobility, a real-world measure of level of service, can be seriously reduced.
The BCI makes a deduction in its rating linearly in proportion to motorist speed. The BCI therefore fails to measure the difference between bicyclist speed and motorist speed, as already mentioned, but it also rates streets higher as the motor traffic becomes more congested and increasingly impedes bicycle travel.
The implementation paper indicates that the BCI is supposed to be used only with outside lane motor vehicle traffic flow between 90 and 900 vehicles per hour; outside lane width between 3.0 and 5.6 meters; bike lane/shoulder width between 0.9 and 2.4 meters; and motorist speeds between 40 and 89 km/h (25 and 55 mph). The speed and flow ranges exclude many conditions typical of congested urban traffic.
If the person applying the BCI does not keep the data range limits in mind, it is very likely that out-of-range data will be input. If the formula is applied automatically to GIS data, results based on out-of-range data are almost certain to go undetected.
The following examples (for which data are given in a table, below), illustrate the inaccurate results the BCI gives under some typical urban traffic conditions that produce out-of-range data.
The table below shows results which the formula gives under several conditions with data in range and out of range. Only the data fields which change are shown. The calculations including all data fields are included in a Microsoft Excel workbook made available in connection with this article.
In the upper rows of the table, gridlocked traffic rates a higher LOS than moving traffic, whether or not there is room on either side of the gridlocked travel lane for bicyclists to overtake freely.
The bottom few rows illustrate the failure to account for overtaking on the left of stopped traffic. Note that a bike lane increases the rated level of service, despite the issues raised earlier about overtaking on the right.
Table comparing levels of service calculated
according to the Bicycle Compatibility Index
(some with parameters out of range)
|Midblock Identifier (Route/Inter-
secting Streets, Segment No., Link No., Etc.)
|Authors' Example: First Avenue - 5th/6th Streets||2||3.6||1.2||37||10000||y||0.30||2.00||B|
|Same but, 5 km/h, 10800 ADT (7m spacing)||2||3.6||1.2||5||10800||y||0.30||1.88||B|
|Same but 0 ADT, 0 speed (gridlock)||2||3.6||1.2||0||0||y||0.30||1.29||A|
|Same but no parking, no parking lane||2||3.6||1.2||0||0||n||0.00||0.79||A|
|Same total width but no BL||2||4.8||0||0||0||n||0.00||1.65||B|
|Same but 3.6.m OL, no BL||2||3.6||0||0||0||n||0.00||2.24||B|
|Same except 3.0m OL||2||3.0||0||0||0||n||0.00||2.54||C|
|Same but 100% pkg, inside lane 30 km/h||2||3.0||0||30||16000||y||1.00||3.83||D|
|2-way 2 lanes, 100% parking, 30 km/h||1||3.0||0||30||16000||y||1.00||5.24||E|
|Same except with bike lane||1||3.0||0.9||30||16000||y||1.00||3.90||D|
Reformatted workbook allows comparisons
The Excel workbook provided as part of the BCI package allows entry of data for only one location. This is a very inefficient and cumbersome use of computer spreadsheet software. I have reformatted the workbook to allow comparison of data for many locations. My revision does not change the formulas, and so it does not solve the problems with the BCI, but rather, helps to reveal them.
I have referenced cells in later workbook sheets to the equivalent cell in the first sheet -- so it is not necessary to type in the name of the location on all three sheets. I also have made cells fit more compactly around the text. Each worksheet will now fit nicely on a 1024 x 768 pixel computer screen at 100% display size. I have also placed the formulas on the new rows inside conditional statements, so error messages will not display unless a location is named.
I have highlighted obligatory data entry cells in yellow, cells in which data may be entered either as a number or as a formula in green, and results in blue. There is one formatting problem I have not corrected: there are four data entry variables in the second worksheet, though the names of the worksheets indicate that only the first sheet is for data entry.
Programming and descriptive errors
In the authors' workbook, one of the data entry cells in the second sheet, for curb lane truck volume, is supposed to default to a different value depending on the number of lanes in the street, but the workbook does not automatically set the default value.
Several header cells describe data entry in percentages where the data must be input as decimal fractions.
There is a serious programming error in the third sheet. The cell for speed (in red) refers to a header cell in the previous row. I have corrected this problem in the rows I have added.
The formula, as I have corrected it, carries an assumption that the 85th percentile speed of traffic is 15 km/hr faster than the speed limit, if an actual 85th percentile speed is not given. Though the report indicates that the 15 km/h adjustment can be altered, it must be altered in a formula rather than in a table cell. If an 85th percentile speed of zero (out of range but common in urban areas) is entered, the formula will "correct" this to 15 km/h.
As already noted, the workbook does not post error messages if numbers are posted for conditions outside the range which the BCI is supposed to account for. As many common traffic conditions are outside its range, I have not attempted to correct this problem in my revised workbook, because I want users to be able to test the BCI with out-of-range data.
There are data cells with range limitations imposed by hard mathematical limits -- for example, parking occupancy can not be higher than 1.00 or lower than 0.00. These cells, too, would benefit from error trapping, to prevent input of invalid data.
I have highlighted the cells with outright programming and descriptive errors in red, and I have highlighted cells with range limitations that are within the range of normal traffic data in purple.
Conclusions and recommendations
While a level of service rating is a useful tool, the Bicycle Compatibility Index is not a level of service rating, and it is flawed as a comfort rating. It is remarkable that the FHWA has sanctioned this work in the light of other highly advanced research into traffic flow that it has generated.
How could a better bicyclist level-of-service rating be developed? That question is difficult to answer. Let us consider the three primary elements of a rating: mobility, safety and comfort.
Workable ratings of bicycle routes have been produced by experienced bicyclists. Though objective factors such as traffic counts, motor vehicle speeds, lane widths and steepness of climbs play an important part in such ratings, there are other important factors which, though objective, do not show up in the usual highway department databases -- for example, quality of pavement near the edge of the road, or the availability of roadside amenities. A good route surveyor will be familiar with the type of bicyclist who is to use a route -- indeed, must have experience with the type of cycling that is to be accommodated. The surveyor also must travel the route to experience it firsthand. In the end, a rating may be based to a large degree on factors that were not even considered before surveying the route, and which would require an impractical, complicated data structure to quantify. The rating therefore becomes to some degree subjective. Despite these problems, the success of ratings developed by and for bicyclists is shown, for example, by the low crash rate on the Bikecentennial TransAmerica route. Such ratings are, in the author's opinion, the best ones available.
 University of North Carolina Highway Safety Research Center (1998) Development of the Bicycle Compatibility Index: A Level of Service Concept, Final Report, FHWA-RD-98-092. http://safety.fhwa.dot.gov/fourthlevel/pdf/bcifinalrpt.pdf or http://www.hsrc.unc.edu/research/pedbike/98072/index.html
 University of North Carolina Highway Safety Research Center (1998) The Bicycle Compatibility Index: A Level of Service Concept, Implementation Manual, FHWA-RD-98-095. http://safety.fhwa.dot.gov/fourthlevel/pdf/bci.pdf or http://www.hsrc.unc.edu/research/pedbike/98095/index.html
 Pein, Wayne. (2003) Critique of FHWA Bicycle compatibility Index. http://humantransport.org/bicycledriving/library/critique_BCI.pdf
 Microsoft Excel workbook in the Bicycle Compatibility Index: A Level of Service Concept, Implementation Manual, http://www.hsrc.unc.edu/research/pedbike/98095/BCILOS/BCIEQUTN.XLS
Acknowledgements: I thank Wayne Pein and John Forester for their helpful comments.