The City of Boston's Hackney Carriage Rules [PDF], section 5.II.y: Passenger’s
Right to Direct
Route: Hackney Carriage Drivers shall take such route to the destination as the passenger shall so direct.
So you are absolutely allowed to declare your own route, and the driver must follow it.
The Rules explain what recourse you have if they refuse.
NYC has a similar rule, and I imagine other cities do, as well.
travel.stackexchange.com/users/1301/kevingessner
I always do it if I think the route is not optimal.
You are paying the bill after all!
travel.stackexchange.com/users/44/Grzenio
Cabbies almost always choose the route they think is going to be the quickest, not the shortest.
That's because a busy cabbie will lose money whenever they are stuck in traffic - the extra on the meter for stopped time doesn't make up for the fact that they could be getting another fare.
So if you try to direct them to a shorter but slower route they will complain (it's also unlikely that you will save money).
Some cabbies will try to take you a long route if they think they aren't going to get another fare, to get more money from you.
In either case the route should be up to you - although that doesn't mean they will be happy about it.
If you really think the cabbie is ripping you off you shouldn't worry about 'etiquette'.
The exception is if you've agreed a fixed price in advance.
Then you should leave the route to the driver.
They will want to do it as fast as possible anyway.
travel.stackexchange.com/users/264/DJClayworth
If you don't want to get into a long discussion about which route is quicker at this time of day, you can always invent an innocuous reason.
"Could you go via the park?
I'd like to see whether the trees are in leaf yet/ past the museum?
I'd like to see what the queue is like for the exhibition.
" You're not challenging the driver's ability, and if you're paying, he can't really object.
travel.stackexchange.com/users/3576/Tim Lymington
I usually open the conversation with a knowledgable-sounding comment on the traffic: "What would b the best route at this time - over the bridge, or through the tunnel".
I just make sure first that there is a bridge or tunnel in that city.
Last week in Milan, Italy, I had the experience of substantially longer routes taken by the taxi driver, and I would just pull out Google Maps on my mobile phone and say -
can you help me follow along.
This technique helped in both instances.
In many cities, fixed fares to the airport are available from hotels and business districts and are usually reasonable and both parties are happy.
travel.stackexchange.com/users/3575/Akber Choudhry
Yes you can.
The customer is king.
But it's not sure that the customer will save money by doing that.
Also note that the shorter route is not necessarily the fastest.
It depends on traffic conditions.
travel.stackexchange.com/users/11860/Maître Peseur
I don't see why not.
I used to live across the Mississippi River from the Metrodome in Minneapolis.
Once I took a cab to the Metrodome.
The driver turned to go down town, a long way to get to the Metrodome.
I asked the driver if there was a good reason for going downtown when the tenth avenue bridge would have taken us right to the Metrodome.
The driver turned off the meter and took us to the Metrodome.
travel.stackexchange.com/users/3594/Jay
This is probably the first time in my life I've heard 'taxi' and 'etiquette' mentioned together in a sentence!
However, I don't think its a form of etiquette, think of it as professional courtesy.
You both know the city and if you're certain about your route, it should at least be open for debate.
At least, that's my opinion.
travel.stackexchange.com/users/3572/Digitalis
I once instructed a taxi to drive miles on surface streets from JFK to Brooklyn instead of any parkways.
I checked that I was entitled to do so.
It was much shorter.
The flight had landed about 5:30 a.m., we were going to a Bat Mitzvah at 10:00 a.m., and then back to the airport for the final leg of our flight in the evening.
Even missing every light we we three hours early for the ceremony, and the cabbie was not very happy.
travel.stackexchange.com/users/18431/Andrew Lazarus
I'm going back home to Virginia for the Thanksgiving holiday and I'll be taking a taxi to Boston Logan. I've noticed that in the past, the cabbie tends to take a longer route.  Is it bad etiquette to dictate which route I'd like him/her to take?
Can you tell a cabbie which route to take?
travel.stackexchange.com
<routes><taxis><boston>
travel.stackexchange.com/questions/10714
travel.stackexchange.com/users/3569/Miriam
You are allowed to declare your own route, and the driver must follow it. Fixed fares are also available from hotels and business districts to the airport, which are usually reasonable to both parties. Most people think it is OK to tell a taxi driver which route to take, however, in some cities, there are routes with fixed prices, like hotel to airport, where it would be unnecessary to dictate the route.
Most people think it is OK to tell a taxi driver which route to take. In some cities there are routes with fixed prices, like hotel to airport, where it would be unnecessary to dictate the route.