Details:

Creators:
Lan, Bo ; Srinivasan, Raghavan
Lan, Bo ; Srinivasan, Raghavan Less -
Corporate Creators:
United States. Federal Highway Administration. Exploratory Advanced Research Program ; Highway Safety Information System
United States. Federal Highway Administration. Exploratory Advanced Research Program ; Highway Safety Information System Less -
Corporate Contributors:
United States. Federal Highway Administration
Subject/TRT Terms:
[+]
Flashing Traffic Signals Highway Safety Information System HSIS Signalized Intersections Traffic Accidents Traffic Safety Traffic Signal Phases
Publication/ Report Number:
FHWA-HRT-13-069;HRDS-20/08-13(750)E
Resource Type:
Tech Report
Geographical Coverage:
United States;Michigan;North Carolina
TRIS Online Accession Number:
01494726
Corporate Publisher:
United States. Federal Highway Administration
Abstract:
During late-night flash (LNF) mode (from late night to early morning hours), traffic signals flash yellow for one road (typically, the major road), requiring caution but no stopping, and flash red for the other road (typically, the minor road), requiring drivers to stop and then proceed through the intersection after yielding to the traffic on the major road. The intent of LNF is to reduce energy consumption and delay during periods of low traffic demand. However, in recent years, many agencies have begun replacing LNF with normal phasing operation because of safety concerns. The safety impacts of replacing LNF with normal phasing operation have been studied since the 1980s. Gaberty and Barbaresso analyzed crash data at 59 four-leg intersections in Oakland County, MI, where the nighttime flash mode was replaced with normal phasing operation.(1) Results indicated a 91-percent reduction in angle crashes and a 95-percent reduction in injury right-angle crashes. However, it was not clear whether high-crash locations were selected for the change and whether the results may have been biased due to regression to the mean (RTM). Similarly, Polanis evaluated the safety of removing LNF from 19 sites in Winston-Salem, NC, using a naïve before-after method and concluded that nighttime right-angle crashes decreased by 78 percent.(2) Srinivasan et al. conducted a before–after evaluation of LNF conversion using the empirical Bayes (EB) method based on a small sample of 12 intersections in Winston-Salem, NC.(3) The EB method was used to specifically address the possible bias due to RTM. The authors concluded that nighttime crashes decreased by 35 percent, and nighttime angle crashes decreased by 34 percent. More recently, Murphy conducted an evaluation of 67 intersections in North Carolina using a before-after EB method but without using data on traffic volumes.(4) Murphy found that for sites where LNF was discontinued, there was a 27-percent reduction in nighttime crashes, a 23-percent reduction in injury and fatal crashes, and a 48-percent reduction in frontal-impact crashes.(4) It is clear that while all the previous studies seem to indicate that removing LNF (and replacing it with normal phasing operation) will reduce crashes at night, each study had at least one limitation- possible bias due to RTM was not explicitly addressed, the sample was small, or traffic volumes were not considered. The objective of this effort was to evaluate the effect of eliminating LNF operations at signalized intersections using state-of-the-art methods and to address the noted limitations. The goal was to include an adequate sample of locations for which traffic volume data were available.
Format:
PDF
Collection(s):
Federal Highway Administration
Main Document Checksum:
[+]
urn:sha256:19ef25892b438ca8388691102630c992aafed16c7f7ff628a54069fc1e0f9d5a
Download URL:
https://rosap.ntl.bts.gov/view/dot/34851/dot_34851_DS1.pdf
File Type:

Supporting Files

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