ITE Journal March 2018 - 41

This article analyzes traffic impacts from a 2015 implementation of
a road diet along Lincoln Avenue, in the City of San José, CA, USA
to answer the following questions:
1. How did the road diet impact all-day counts of traffic volumes
and speeders for each street type?
2. How did the road diet impacts vary by street type when looking
at all-day counts versus data for peak hours and data by hour of
the day?
3. What are recommended best practices for conducting and
presenting road diet evaluations that look at speeding and traffic
volume impacts?
More detailed study findings are documented in Nixon et al.,
2017.3

About the Lincoln Avenue Road Diet Project
Lincoln Avenue is a major arterial running through the Willow
Glen neighborhood in San José, California. Willow Glen is a
relatively affluent, predominantly residential neighborhood with
a small neighborhood business district. The street, a four-lane,
undivided roadway, has become a popular route for commuters
avoiding the more congested nearby freeways and expressways.
Close to 20,000 vehicles per day travel along this route, often above
posted speed limits.
In response to neighborhood concerns about traffic, city staff
designed a one-mile (1.6 km) road diet to reduce through traffic lanes
from four to three, using the space freed up from the fourth travel
lane to create marked bicycle lanes (Figure 1). Because the project
faced considerable controversy, the city implemented the diet as a
pilot project and conducted an extensive evaluation. The pilot ran a
full year, from February 2015 to February 2016, and the evaluation
was the most extensive data collection effort ever undertaken by San

José's Department of Transportation. In June of 2016 the San José
City Council voted unanimously to make the road diet permanent.

Data Collection and Analysis Methods
This study analyzed data obtained from the City of San José's
Department of Transportation, which had collected traffic volume
and speed data using pneumatic road tubes placed at 45 locations
in the Willow Glen neighborhood. The locations were distributed
throughout the neighborhood, across four different "street types,"
as follows:
ƒ Lincoln Avenue road diet: 2 locations within the road diet
implementation zone;
ƒ Lincoln Avenue non-road diet: 4 locations along Lincoln Avenue
outside the road diet area;
ƒ Major streets: 16 locations along major roads within Willow
Glen; and
ƒ Neighborhood streets: 23 locations along neighborhood streets
thought most likely to be impacted by the road diet because
they were close to Lincoln Avenue or likely to serve as an
alternate route.
Data were collected on traffic volumes and speeds over three
weekdays before the implementation of the road diet in February
2015 and again one year later in February 2016.
The analytical approach taken here focuses on descriptive
changes in traffic volumes and speeds across the four types of street
location-the Lincoln Avenue road diet segment, Lincoln Avenue
non-road diet segment, major streets, and neighborhood streets.
(For a detailed analysis of all 45 individual locations and discussion
of key localized impacts, see Nixon et al., 2017. 3)

Findings
This section looks first at how the road diet impacted traffic
volumes and then at the impact on the number of speeders. Each
subsection starts with a look at the most aggregated data-all-day
data averaged for all locations in each street type-and then moves
to a more nuanced look at the impacts by time of day.

Traffic Volume Impacts

Source: Nixon et al., 2017.3

We analyzed volume impacts in two different ways: mean values
for each street type, considering both all-day volumes, and also
impacts by time of day (peak-hour volumes and volumes for each
hour of the day).

All-Day Impacts

Figure 1. Illustration of a 4-lane to 3-lane road diet.

Data in the first row of Table 1, showing all-day traffic volumes
before and after the road diet, suggest that the road diet did not
divert traffic to other streets in the neighborhood. Although
volumes fell noticeably at the Lincoln road diet collection points
w w w .i t e.or g

M arch 2018

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Table of Contents for the Digital Edition of ITE Journal March 2018

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