If you live in North Cambridge or travel via Massachusetts Avenue north of Porter Square, you’ve probably seen the city’s new dedicated bus lane and protected bike lanes, and you might have had some questions:

• What are the bus lanes good for?
• How many people really take the bus? It only goes by very infrequently.
• Traffic was already bad; won’t this make it worse?
• Why do we need dedicated bus lanes?

To understand the benefit of these bus lanes, you first have to realize how much more efficient buses are at moving people. A bus might be three times as long as a car, but compared with a single-occupancy vehicle with just one driver, it can carry 40 times as many people. Put another way, buses can often move 13 times as many people using the same amount of space as cars.

To give a real example, a study done on Mount Auburn Street during rush hour showed buses were only 3 percent of vehicles but carried 55 percent of the people on the road!

Since they are moving so many people, a bus stuck in traffic affects far more people than just a single car. Additionally, getting stuck in traffic can increase the variability of bus arrival times, which means passengers need to plan not just for trip time but also for the worst-case delay caused by variability. Which makes the impact even worse.

This is why we need dedicated bus lanes, separate from normal vehicle lanes: They speed up the bus and reduce variability for a very large number of people at once, even if the number of vehicles is small. In the end, people are important, not vehicles.

If traffic wasn’t bad, there would be no need for dedicated bus lanes. So by their nature, dedicated bus lanes need to be built on congested streets. As far as the impact of these lanes, the city estimates that in the long run these changes will add only two to three minutes to car drivers’ rush-hour commute. That being said, based on other bus lanes across metro Boston, in the long run there might be almost no additional delays for vehicle traffic once everyone gets used to the new lanes.

On the Broadway, Somerville, dedicated bus lane, travel times for motor vehicles were almost identical to times before implementation, and overall motor vehicle volumes decreased. As in this project, traffic models projected an increase in travel times on Broadway but, due to a shift to more people riding the bus and biking and drivers adjusting their routes, these projections did not materialize.

In general, we have seen from the many bus lane projects across the region that when bus lanes are introduced, bus ridership goes up. Examples of this improvement include Broadway in Somerville, where ridership increased by 36 percent to 69 percent and Brighton Avenue in Boston, where ridership increased by 5 percent to 8 percent. Both roadways are similar in terms of width and vehicular traffic counts to North Massachusetts Avenue. And this is one of the streets the MBTA is considering for higher-frequency service, which will be enabled by dedicated bus lanes – allowing even more people to ride it. And more people riding the bus means fewer people driving.

Do we really need dedicated bus lanes on this particular stretch?

The 77 bus that goes through the northern section of Massachusetts Avenue continues to be one of the top-20 ridership routes in the MBTA system, with almost 7,500 riders on weekdays in 2019. And even as it is one of the busiest routes in the region, it is also one of the more unreliable routes in Cambridge.

Failing bus service is one of the greatest disparities threatening our region. Transit inequities lead to Black riders spending 64 more hours per year on the bus compared with their white counterparts. Per the 2017 MBTA survey of route 77 riders:

• 35 percent of riders were low-income.
• 24 percent were minority riders.
• 57 percent were women.
• 13 percent were seniors.
• 32 percent didn’t own a car.

A faster bus means seniors can spend less time waiting in the cold for a late bus and parents can spend less time commuting to work and more time with their children. Thousands of bus riders will have a faster ride every day. And as more people switch to riding this now faster and more reliable route, we will all benefit from less congestion and cleaner air.

Jarred Johnson is executive director of the transportation advocacy group TransitMatters, and Matthew Petersen is its programs manager. Kristiana Lachiusa is director of transit and outreach for the LivableStreets Alliance, a Cambridge nonprofit.