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Selecting an Appropriate Treatment 27
3.5.7 Documented Applications, Speed Effects, and Safety Effects
The columns for documented applications, speed effects, and safety effects in Exhibit 3-6
describe the tested applications for which the listed documented speed and safety effects were
achieved. This information should be considered to determine the extent of research and data
on a particular treatment and to identify similarities and differences in the tested applications
that may produce similar or dissimilar effectiveness in a candidate site under consideration.
3.5.8 Key Considerations
Many treatments are likely to have significant impacts on multimodal users, site-specific
maintenance considerations, and/or other issues that should be considered as part of the screen-
ing process. These secondary impacts may be limiting factors depending on the context for
installation. For example, maintenance concerns related to snow removal will be significant in
some environments and insignificant in others. Conditions in which particular treatments are
not advised also are key considerations.
3.6 Treatment Evaluation
Monitoring and evaluating the effectiveness of treatments can provide valuable data and feed-
back for determining appropriate treatments for future applications.
3.6.1 Speed Monitoring
Speed monitoring is the most direct way to evaluate the effectiveness of a speed reduction
treatment. To evaluate speed effects, before-and-after data should be collected and compared.
Driver acclimation effects can be expected with many of the treatments; therefore, the after-data
collection should be targeted to identify both short- and long-term effectiveness. Speed moni-
toring can also be used to evaluate how effective treatments are under particular weather or light-
ing conditions.
Data collection efforts should consider the driver behavior desired on the intersection
approach, and should target data collection to determine to what extent the desired behavior has
been achieved. In most cases, speed reduction is desired not only at the intersection proper, but
on the approach as well. Collecting speed data at several points on an intersection approach will
give the best picture of drivers' deceleration curves (a speed profile) as they respond to the treat-
ment(s) approaching the intersection. Appendix B identifies the speed data collection points for
several case studies. Additional information about speed testing programs can be found in the
testing results section of NCHRP Web-Only Document 124.
3.6.2 Safety Monitoring
As stated repeatedly in these Guidelines, there are no data to support the use of speed as a sur-
rogate for safety or vice versa. An improved safety record based on implementing one or more
of these treatments does not necessarily indicate that speeds were reduced. Nevertheless, safety
is a critical concern for transportation professionals, and monitoring the safety effects of these
treatments may be desirable.
Safety effects must be monitored and analyzed over a period of several years before any sig-
nificant conclusions can be drawn. Crashes are infrequent events and extensive data are needed
to evaluate improvements in safety performance.
