We all know that most of the north and south avenues of Manhattan in particular are engineered to have lights turn green in a cascading order, but what may help triple your time is finding the crosstown streets that also have green lights proceeding in an orderly fashion.
56th Street through 59th Street go very well across Manhattan from west to east, 57th street in particular if there is no construction will send you to the Upper Roadway of the bridge in the cleanest smoothest style. I am not so sure about the even numbers 46 through 54, they may be pretty good too, but nothing is as good as 57th.
I just took 36th street to the Midtown Tunnel today, and it wasn't bad, but not so good either, 40th street goes really well. Traffic will be a problem as the day gets full of double-parkers and unloaders, and 38th I've known to run all green from 11th avenue all the way to 2nd avenue where you turn right and find the entrance at 36th street for the Queens Midtown Tunnel. Both 36th Street and 38th Street have double lanes so you can steer around people who look for parking.
Now a bus driver told me about this one, are you ready? From Madison Avenue, 34th street goes green in both directions, west from Madison, and east from Madison. Again use your best judgement, but quite surprisingly, 34th Street from Madison Avenue I rarely find to have traffic complications. 34th is only bad into Madison Ave, away from Madison is good I've found.
The other crosstown streets are dodgy, 23rd Street is a good east bound street. Much like 57th, both 22nd street and 26th street also go well eastwards, however the chances you will get stuck behind some slow poke from the suburbs, or a police car is highly likely on 22nd and 26th. Everybody in Greenwich Village on Hudson, or Chelsea on 8th Avenue, will want you to take 23rd street if their destination is above 23rd and on Madison Avenue or further east.
14th street goes sort of well in the west direction, 13th street goes even better, but forget about taking the small 13th street once traffic gets hefty, and watch the speed bumps. 11th street from University I once took with great green light success, but I don't remember the last time it went so well, so give us an update on how that one works. The elementary school is on 11th street between 6th ave, and 7th, so beware of complete blockage during school opening and closing.
On that note 85th street in the Upper East Side, while it goes really well to the west, has a fire station, and everybody and their Volvo gets stuck when that truck goes out or comes in. Some people prefer you take 86th street across to 5th Avenue and cross the park at 85th there.
Similarly 29th Street is an absolute gem of a street going west to 6th avenue to get to the 31st Street or 33rd/32nd Street entrances of Penn Station on 7th Avenue, BUT once everybody has woken up and started their day (after 7am) that street looses its mojo and you're better of getting to 6th avenue to head uptown as soon as possible, there really is no good way to Penn Station. If your passenger deems it okay, it will tend to be an easier ride to the 8th Avenue side. We all know how bad 6th Avenue can get. asking first, and bringing our customers up 8th Avenue saves us time, it saves them money, and is much less of a taxi ticket trap.
One of my better luck routes last week was going west on from the FDR Drive to 34th Street and 3rd Avenue. I proceeded west on 35th street, making a left on the midtown tunnel exit service road, then a right on 34th Street. It was surprisingly awesome, but again, if you can avoid all of that it'd be best to, most of the time the 30's and the 50's get real bad heading west. 35th street and 37th are extremely bad and tend to cause gridlock.
Delancey/Kenmare/Broome combo is an awesome combo of green lights going west all the way from the Williamsburg Bridge to the Holland Tunnel (make a left at Laffayette, and a right at Broome). Now when everybody has to go back home to New Jersey, it might be best to take Houston Street to Varick. From the Meatpacking district you can take Washington Street all the way to Spring and make the right on Varick, the two right lanes of Varick are for the Holland Tunnel.
Spring Street is a very good street for green lights all the way east, you can take a right at laffayette and a left at Kenmare to get to the Williamsburg Bridge. If you're feeling lucky you can take Spring to Mott to Kenmare, save one light.
New Jersey direct to Brooklyn? just follow the signs out of the Tunnel, it'll dump you on Watts I believe, which merges to Walker, then to Canal, and no matter how much traffic it'll be the best way to The Manhattan Bridge from the west side. I'd tolerate the wait if I were you, the Manhattan Bridge is usually not as congested as the Brooklyn Bridge. But if it's really bad, you may want to deviate and head south on Laffayette for the Brooklyn Bridge.
Chambers runs beautifully west to east, but everyone knows about it and goes that way to take the Brooklyn Bridge. So check out how bad Chambers is, if it's got gridlock (spillover traffic blocking the intersection) than you should take Warren Street to City Hall Park, you are then forced to go south, stay in the left most lane and turn around the park heading back north on park row, now go straight in the two left most lanes to the Brooklyn Bridge.
I hope this isn't too scrambled, I got to get back to work before the meter runs out.
throw in all the comments you can so we can really get a feel for the best crosstown streets