Newbie Questions

[wfisher]

Sorry for the newbie question but I've had this question for a while and I called NJ Transit but they never responded. Does anyone know how they determine their timetables and what, if any, scheduling algorithms they use to balance demand and resources?

 

Another question about rail: does anyone know why trains start up (accelerate) so much slower than subway cars? Is it that they weigh so much more or that their motors are weaker? Subways start so fast but trains accelerate from stations very slowly it always seems.

 

Thanks!

[kaback9]

I'll take a crack at both.

 

Timetables at least with the North East Corridor, North Jersey Coast Line and the M&E trains to NYP are done based on what time slots are made available by Amtrak.

 

The trains start up slowly except for the Arrow III's slowly because a single unit pulling or pushing an 8 car train can't accelerate as fast. When a single engine has anything with 5 cars or less that thing will fly out of the station. Also at least with the new Multilevels and ALP46's there is a wheelslip problem. That would cause a slow acceleration.

[metsfan]

Correct, however there's one huge difference between subway & main line rail. The difference being the speed & weight of trains. Subway car might weigh a full 3rd less than a push/pull car just because its smaller in every dimension including the motors. The trucks are bigger and have a longer space on the track on main line pax vehicles. Also a normal 12 car train with alp-46 up front is 1090 feet long vs subway is 600 or something.

 

Now, weight is one thing, then there's the speed. If an alp-46 were to somehow get a full length subway train on the :nec: you could, if the alpy was geared right, pull that 600 foot long subway train at ~135 mph. There's no way a subway car could ever go over about 80 without derailing. They did tests on the LIRR before they changed the voltage to this effect and stopped short of derailing with a 75 foot car.

 

As far as acceleration, correct also, distributed traction gets the vehicle going more quickly. If a locomotive pushing or pulling a train floors it, you'll see huge shower of sparks as the wheels spin against the rails. A talented engineer can get even the longer trains going pretty fast by riding that fuzzy traction/slip edge letting the locomotive's anti-slip features work to keep it in the green. Some of the older locomotives such as the alp-44 and the older aem-7 have less advanced traction tech & you will feel slipping & surging as the wheels either spin too fast for the momentum of the train & make no progress, or catch when its slipping & jerk the whole train forward. Just slip feels like a momentary deceleration, while a surge is more noticeable with a very short moment of deceleration with a sudden jolt in the direction of vehicle/train movement.

 

EMU, which is what subway cars are really, have good stop/start because of distributed traction. The space under the cars however limit transformer size therefore limit the power of the electric motors. You'd need AC to get higher speeds & AC = transformers.

 

Locomotive or power car moved trains are more focused on longer spaces between stops, however often have a higher speed because you have one dedicated unit to do all of the work.

 

- A