Time Spent in Congestion

How much time do Bay Area drivers spend sitting in traffic?

Time Spent in Congestion

Definition: 
Time spent in traffic congestion – also known as congested delay – refers to the number of minutes weekday travelers spend in congested conditions in which freeway speeds drop below 35 mph. Total delay, a companion measure, includes both congested delay and all other delay in which speeds are below the posted speed limit.

Everyone has been there – cruising along at 65 mph only to see a sea of brake lights up ahead in the distance. Traffic congestion is frustrating to drivers, affecting mobility between cities and counties of the Bay Area. At the same time, congestion is usually a byproduct of favorable economic conditions, and many of the nation’s most vibrant metropolitan areas struggle with congestion.

Congested delay occurs when speeds drop below 35 mph. When speeds fall below this threshold, the freeway corridor begins to operate inefficiently as its capacity declines. While travelers are delayed when speeds are lower than the speed limit (e.g., 55 mph in a 65 mph zone), this is not defined as congested delay as the freeway is actually operating more efficiently at this speed.

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Regional Performance
The region’s current economic boom has pushed congestion levels to record highs for the fourth consecutive year.

Freeway delays due to congestion have increased 9 percent from 2015, averaging 3.5 minutes per commuter in 2016. Notably, regional traffic congestion is significantly worse compared to previous economic booms. Since the peak of the dot-com boom in 2000, per-commuter congested delay has skyrocketed by 64 percent, while population has grown by 13 percent and jobs have grown by 8 percent. This trend is particularly noticeable for Bay Area drivers given that nearly all of the growth in gridlock has occurred during the last four years. Commuters are likely also experiencing delays on arterials and local roads, although there is insufficient data to quantify these trends.

Historical Trend for Time Spent in Highway Congestion — Bay Area

Local Focus
Bay Area freeway congestion is heavily concentrated in a handful of key corridors – most notably, the Bay Bridge corridor.

While congestion only generates a few minutes of delay for the average commuter, commuters in a handful of high-demand corridors experience far worse conditions. The top ten most congested segments constitute nearly half of all regional freeway congestion, with just two top segments along the Bay Bridge corridor constituting 16 percent all Bay Area traffic congestion. Notably, all ten of these congestion hotspots are affecting the evening commute for the first time on record. While many of these corridors are no surprise to Bay Area drivers, State Route 4 has re-emerged as one of the most congested routes in the region, despite efforts to add capacity in recent years.

Over three-quarters of all congested delay on the Bay Area’s freeway network occurs in Alameda, Contra Costa and Santa Clara counties. Of those counties, Contra Costa County saw the largest rise in hours of congestion with a 27 percent increase compared to 20 percent growth in Santa Clara County and 13 percent growth in Alameda County. The North Bay remains relatively immune from recurrent congestion, accounting for only 5 percent of total delays on a typical weekday – most of which is concentrated on U.S. Route 101 in Marin County.

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2017 Time Spent in Highway Congestion

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Select a congested segment on the map for more information.

Most congested segments

1. US-101 northbound & I-80 eastbound from Cesar Chavez to Treasure Island Tunnel
2. I-80 westbound from Hercules to Bay Bridge Toll Plaza
3. US-101 southbound from Mountain View to Santa Clara
4. I-680 northbound from Sunol to Milpitas
5. SR-4 eastbound from Martinez to Concord
6. I-80 eastbound from West Oakland to Berkeley
7. I-880 southbound from West Oakland to Fruitvale
8. I-280 southbound from Cupertino to San Jose
9. SR-24 eastbound from Oakland to Orinda
10. I-680 northbound from Danville to Walnut Creek
Sources: 

Metropolitan Transportation Commission/Iteris: Congested Corridor Analysis (2016)

No link available

Metropolitan Transportation Commission: Historical Congestion Analysis (1998-2016)

No link available

Texas Transportation Institute: Urban Mobility Report (1998-2014)

California Department of Finance: Population and Housing Estimates

Form E-8 - Historical Population and Housing Estimates (1998-2010)

Form E-5 - Population and Housing Estimates (2011-2016)

California Employment Development Department: Labor Market Information (1998-2016)

Texas Transportation Institute: Unpublished Metro Area Analysis of Severe Congestion Delay (2011)

No link available

U.S. Census Bureau: Intercensal Estimates (2014)

U.S. Bureau of Labor Statistics: Metro Area Employment (2014)

Image: Flickr (Creative Commons license), Photographer: Oran Viriyincy, https://www.flickr.com/photos/viriyincy/4934261108/in/photolist-

Methodology Notes: 

Time spent in congestion measures the hours drivers are in congestion on freeway facilities based on traffic data. In recent years, data for the Bay Area comes from INRIX, a company that collects real-time traffic information from a variety of sources including mobile phone data and other GPS locator devices. The data provides traffic speed on the region’s highways. Using historical INRIX data (and similar internal datasets for some of the earlier years), MTC calculates an annual time series for vehicle hours spent in congestion in the Bay Area. Time spent in congestion is defined as the average daily hours spent in congestion on Tuesdays, Wednesdays and Thursdays during peak traffic months on freeway facilities. This indicator focuses on weekdays given that traffic congestion is generally greater on these days; this indicator does not capture traffic congestion on local streets due to data unavailability.

This congestion indicator emphasizes recurring delay (as opposed to also including non-recurring delay), capturing the extent of delay caused by routine traffic volumes (rather than congestion caused by unusual circumstances). Recurring delay is identified by setting a threshold of consistent delay greater than 15 minutes on a specific freeway segment from vehicle speeds less than 35 mph. This definition is consistent with longstanding practices by MTC, Caltrans and the U.S. Department of Transportation as speeds less than 35 mph result in significantly less efficient traffic operations. 35 mph is the threshold at which vehicle throughput is greatest; speeds that are either greater than or less than 35 mph result in reduced vehicle throughput. This methodology focuses on the extra travel time experienced based on a differential between the congested speed and 35 mph, rather than the posted speed limit.

To provide a mathematical example of how the indicator is calculated on a segment basis, when it comes to time spent in congestion, 1,000 vehicles traveling on a congested segment for a 1/4 hour (15 minutes) each, [1,000 vehicles x ¼ hour congestion per vehicle= 250 hours congestion], is equivalent to 100 vehicles traveling on a congested segment for 2.5 hours each, [100 vehicles x 2.5 hour congestion per vehicle = 250 hours congestion]. In this way, the measure captures the impacts of both slow speeds and heavy traffic volumes.

MTC calculates two measures of delay – congested delay, or delay that occurs when speeds are below 35 miles per hour, and total delay, or delay that occurs when speeds are below the posted speed limit. To illustrate, if 1,000 vehicles are traveling at 30 miles per hour on a one mile long segment, this would represent 4.76 vehicle hours of congested delay [(1,000 vehicles x 1 mile / 30 miles per hour) - (1,000 vehicles x 1 mile / 35 miles per hour) = 33.33 vehicle hours – 28.57 vehicle hours = 4.76 vehicle hours]. Considering that the posted speed limit on the segment is 60 miles per hour, total delay would be calculated as 16.67 vehicle hours [(1,000 vehicles x 1 mile / 30 miles per hour) - (1,000 vehicles x 1 mile / 60 miles per hour) = 33.33 vehicle hours – 16.67 vehicle hours = 16.67 vehicle hours].

Data sources listed above were used to calculate per-capita and per-worker statistics. Top congested corridors are ranked by total vehicle hours of delay, meaning that the highlighted corridors reflect a combination of slow speeds and heavy traffic volumes (consistent with longstanding regional methodologies used to generate the “top 10” list of congested segments). Historical Bay Area data was estimated by MTC Operations staff using a combination of internal datasets to develop an approximate trend back to 1998.

To explore how 2017 congestion trends compare to real-time congestion on the region’s freeways, visit 511.org.