4 min

HOV Lanes: Congestion Relief or Traffic Headache?

More cars mean more problems for cities. The biggest issues? Congestion and CO2. High-occupancy vehicle (HOV) lanes offer a potential path to reduction but come with pros and cons. Here's a look at HOV basics, their benefits and drawbacks, and what comes next for congestion relief.


27 Jun, 2023

The Problem With Personal Transportation

According to the Environmental Protection Agency (EPA), personal passenger vehicles emit approximately 4.6 metric tons of CO2 each year. Worldwide, these vehicles account for 45.1% of transport emissions.

When it comes to congestion, meanwhile, more vehicles on the road means longer wait times for commuters to get where they're going. Consider that in the United States, traffic congestion cost the country more than $81 billion in 2022, and American drivers spent 51 hours on average last year stuck in traffic.

HOV Lanes: The Basics

HOV lanes are one approach to reducing personal vehicle volumes. The concept is simple: Cities designate specific lanes of traffic as high-occupancy. Vehicles with the requisite number of people — two, three, or more, depending on the lane — are allowed to use the HOV lanes. In theory, this both reduces the number of vehicles on the road and gets those in HOV lanes where they're going faster.

These lanes are typically identified by diamond symbols on signs or pavement. Vehicles with only one occupant using the HOV lane may be subject to fines or penalties.

Pros of HOV Lanes

Proponents of HOV lanes point to benefits such as reduced greenhouse gas emissions and improved commute times. According to a study from the University of Colorado Boulder, "On average, encouraging HOV lane use is beneficial for moderate levels of reduced demand."

If lanes are clearly marked and enforcement is consistent, these lanes can decrease the amount of time drivers and passengers spend on the road and reduce the total number of vehicles on the road. It makes sense: Why not carpool with coworkers if the drive is shorter and you can save money by splitting the cost of fuel?

Cons of HOV Lanes

There are also potential drawbacks to HOV lanes. The most common con argument is that HOV lanes don't actually work. Opponents say that HOV lanes take up space that could be used for additional, regular traffic lanes and point to issues of inequality: Travelers who can't carpool or use public transportation can't access HOV lanes, meaning these lanes may not be used to their full potential. The CU Boulder research makes it clear that while HOV options can make a difference, "there is substantial variation across and within routes."


What's Next for Congestion Relief?

HOV lanes remain a work in progress. In states like Nevada, the Department of Transportation has introduced HOV schedules — lanes are only reserved for high-occupancy vehicles during peak congestion hours. Research efforts are also underway to find optimal HOV configurations. One option is the use of "contraflow" lanes, which run opposite the normal flow of traffic on their side of the road. Recent research found that using a full contraflow system increased average vehicle speed in congested areas by more than 10 miles per hour.

It's also possible to improve the use of HOV lanes by integrating high-occupancy lane data into in-car navigation and mapping tools. If drivers are given routes that include available HOV lanes and reduce their overall travel time, they're more likely to seek out carpool opportunities. For example, NNG's iGO Navigation integrates HOV data to provide information about where HOV lanes are located, and when they are active. Our GREEN and ECO route planning methods, meanwhile, optimize fuel consumption by accounting for route factors such as elevation, wind drag, and the availability of HOV lanes.

While HOV lanes haven't solved the traffic crisis, they still have value as part of larger efforts to reduce congestion and limit greenhouse gas emissions. By implementing schedules that favor HOV use, creating designs that improve HOV efficiency, and leveraging in-vehicle navigation tools that take into account HOV routes, cities and drivers can cooperate to enhance environmental stewardship.

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