There's one way to make sure automobiles are driven really fast down a city street: make it one way. You can see it in any city, on any street. Times Square? One-way streets, cabs flying through the Square at 40-50 miles per hour. They're trying to make the next street light before it changes! And just about all streets in Midtown Manhattan are one-way, either East / West or North / South. (I wish I could remember which #s go East and which #s go West but I can't remember. I seem to remember 7th Ave going downtown, so that's South; 8th Ave goes uptown, so that's North.)
Here in Boston, we have a bunch of roads that go in many directions and plenty are two-way and plenty of one way, and for the small, narrow streets, one-way routes don't seem to cause many problems. Historically, I believe that a lot of these small streets, the ones that go through the South End, South Boston, Fenway, and the North End, probably, as well, were two-way, but were converted to one-way at some point. Why? Because the powers-that-be (City Hall, the DPW, residents) wanted to protect their neighborhoods from "outsiders" - whomever that may be. If you drive into the South End, you'll notice there are a good number of one-way streets that take you out of the neighborhood, but few streets that take you into the neighborhood.
There's Columbus, Tremont, Washington, and Harrison that go back and forth, but for streets off these major streets, they tend more than not to go one-way, out of the neighborhood. You can't just loop around to the next street and come back. You're pushed to the edges of the neighborhood so that if you want to get into the city, you have to take a major street to the edge of the neighborhood and start over. (Details, later.)
As mentioned, on narrow streets, especially those with parking on one or both sides, it's not a problem to have one-way streets, because the congestion of cars maneuvering into and out of parking spots, and the narrowness causing cars coming down the street to be cautious, means incoming traffic must slow down. The benefits are, those people maneuvering their cars into and out of spots aren't dealing with crazy people driving their cars at high speeds while they're trying to concentrate. More important, those exiting and entering their cars do not need to fear for their lives while opening their car doors and moving items into or out of their automobiles. An added benefit is that neighbors on the sidewalks can actually cross the street without fearing for their very lives.
But, a wide, one-way city street is a nightmare. I'm talking four lanes or more (although three lanes is a problem, too). A good example of this is Tremont Street facing the Boston Common, in Midtown. The street section in question begins at Government Center, next to the MBTA Green Line / Blue Line station. It's still State Street coming up there, one way, and the road splits with the one to the right heading to Cambridge Street and the one to the left becoming Tremont Street.
Tremont Street, at this point a four-lane street with no parking on either side (there used to be parking on both, actually!), is a one-way street full of cars, taxis, and buses. It's a mad rush to see who can get from Government Center to the Theater District the quickest. There are several lights, but those can be figured out by the drivers so that they reach each just as they are turning green.
There are stop lights and crosswalks for people to cross over to and from Downtown Crossing to the MBTA Park Street Station, but it's a long walk across four lanes of highway, especially in a wheelchair or pushing a carriage.
The one-way road from Government Center to the Theater District (and, beyond) is a great street to use if you want to leave the city quickly. You just drive South sitting in the center lane and zoom your way to Herald Street, a three-lane (one-way) highway that will take you to the on-ramp to the Southeast Expressway.
Instead, Tremont Street should be two-way, the entire way, from Government Center down past the Park Street Church at Park Street, continuing on til it crosses Boylston Street, but continuing on past Stuart Street, up past the Citi Center for the Performing Arts and Shubert Theater, then over the hill and across the bridge spanning the Massachusetts Turnpike Extension, merging with traffic on the one-way Herald Street.
Except Herald Street will also be two way, with an additional lane of traffic opening up where the line of trees run along the side where the MBTA and commuter trains run underneath.
Of the four lanes that from Government Center to the Theater District, two will come South, from the theaters to City Hall; two others will go South, from City Hall to the theaters. Except, only one lane will be for automobiles; the other will restricted to MBTA (and private) buses. (And, if need be and logistics worked out, then cabs and ubers, as well. But only if this doesn't slow down the traffic.)
This should improve the bus transportation system in the area. The two largest bus routes are the Silver Line 1 and 2 that go up Washington Street solely to turn around so that they can come back down Tremont. Making the route roundtrip on Tremont solves that problem, and should make the trips shorter in length and time.
The other major bus line is the Number 43, which does a convoluted route from the South End down Tremont, crosses between the Public Garden and Boston Common, up Beacon, down Park Street, and then drops passengers before it heads off again into the South End, down Tremont Street, around the Mass Pike Towers, and continuing on Tremont Street through the South End and into Roxbury.
The benefits of this are: the routes are the same in each direction; there's overlap. You are picking the bus up, and also exiting the bus, at the same location, just going different ways.
The Number 43, in fact, may not need its own dedicated bus line.
Of course, all of the Silver Line buses will need their own dedicated bus lines. That means, separate lanes with barriers to entry so no automobiles can use them or park in them (like they do in the South End along Washington Street).