So you want to build a bus rapid transit line. In an earlier post, I discussed the various characteristics that have been used to define BRT (or else features of BRT), and concluded that the one most likely to make the difference between "rapid" and "not rapid" is physical separation. But where do you put the physically separated right-of-way?
The answers to this question are roughly the same as for trolleys, so this applies to them too. We're talking about rights-of-way in cities, so there are usually three sources of property that are long enough for a useful transit line: existing or old rail rights-of-way, landfill near waterways, and roads. Occasionally you might have some large chunk of land come on the market, and you can use part of that for a rail line.
Here in New York, there aren't too many existing rail lines with room for new lines. There's been some talk about reactivating or supplementing some rail lines; I may have a chance to talk about them in another post. The Westway case pretty much outlawed landfill for the purpose of building transit. There may be some new transit in the Hudson Yards or other developments, but those aren't necessarily in the areas where transit is needed. That leaves roads.
Converting roads to transit is a political move, and can encounter political resistance. Every road is used by someone, and even the people who use lightly-used roads can object to losing a lane. Part of the reasoning behind "Plan B" is that by rejecting congestion pricing, motorists have refused to pay for the streets they use, and the city is therefore justified in reallocating it to whatever other uses they chose. It's a great principle, but in reality it may not be enough to overcome opposition. In choosing roads to convert to transit use, we should not assume that the Plan B reasoning will be enough to overcome opposition. We should keep in mind that some roads will be easier than others. I'm going to talk about various road widths and how easy or hard they may be to appropriate for transit.
One or two lanes. There exist two-lane busways; I've ridden on the West Busway in Pittsburgh. But the West Busway was converted from a rail line. It runs through a tunnel and a deep gorge with no shops or residences adjacent. Any one-lane or two-lane road that has destinations along it will probably have some people who are used to driving to those destinations, and the shops or residences will be used to receiving deliveries by truck. In Denver, Sixteenth Street was converted to a mall used only by pedestrians and buses, but I believe they still allow delivery vehicles; similarly for the Fulton Street Mall in Brooklyn.
One or two lanes, plus parking, convert the parking lanes to busways. Ensuring access to businesses and residences is the main thing, but people can be very protective of parking, especially in areas where there are more drivers.
Four lanes (or two lanes, one-way), plus parking. Merrick Boulevard in Southeastern Queens has this configuration, and a "BRT" plan has been shelved because of community objections. However, it is important to note that many of the objections were over the taking of parking lanes. The plan did not include physically separated lanes, and in fact the lanes would not have been dedicated to buses 24/7, so the line would not have been Rapid enough to attract proponents.
In streets that have four lanes plus parking, the two middle lanes serve vehicles anticipating turning left, but mainly they allow faster cars to pass slower ones, and increase the overall capacity of the road. They do not contribute as much to the functioning of car traffic as parking lanes do, so taking them for a busway is less likely to engender as much opposition as taking parking lanes. However, opposition can still be considerable.
Six or more lanes (or three or more lanes, one-way), with or without parking. In this case, the additional lanes are not necessary for faster cars to overtake slower ones. They just serve to add capacity and move traffic. Any objection will simply be that "traffic will get backed up." It probably will, but not as disastrously as it can with a simple two-lane road.
Dual-carriageway roads. In this case, there is already some kind of median on the road, which can be used for transit stops. Also, the cross streets are often not extended to the middle carriageway, meaning that transit in the middle can flow better.
Installing transit on the larger streets would also have a traffic calming effect, as has happened where the tramway was installed in Paris. Reducing the number of car lanes reduces the speed of the cars and their ability to change lanes quickly, making things much safer for pedestrians.
Because of this, the most promising road corridors for installation of BRT or light rail are the ones with dual carriageways such as Queens Boulevard, Ocean Parkway and the Grand Concourse. The next most promising are the ones with six lanes or more, like Northern Boulevard, Southern Boulevard and the LIE.
If you really really think that the best place to put BRT is on a two- or four-lane street, you're welcome to try. Just be prepared for some stiff opposition when you tell the local residents and businesses that you want to take away lanes and parking. You may be able to overcome that resistance with data on ridership and time savings, so have it ready.
Of course, buses and trams are flexible, so you could have them running in a shared lane for a short section, but in that section they wouldn't be Rapid.