A few ideas:
1) If 1G acceleration can be maintained, then the speed of light will be reached in 1 year: reference. As such, constant 1g acceleration is not required over the whole distance. Greater accelerations of course result in bursts of energy (I'm calling 1 year a "burst"), rather than a non-stop stream. Keeping a small stream up "lighting up the lane" so the ship knows it is on target might not be bad.
2) Cryogenics and Intersteller-Packing-Foam (which fills the ship and makes it and everything frozen within it much more rigid) could allow for higher accelerations. Higher accelerations, combined with #1 (there is a limited thrust time before reaching C) results in increased transmission times. It also allows for rescue should people/cargo need to wait the ridiculous time frames which would be required for a rescue.
3) Lanes: More shipping lanes, more bandwidth. Each lane is a launch platform, and for various reasons each should be on its own airless planetoid within a solar system. While a solar system may seem big, regarding interstellar distances it is not, as all the lanes will converge on a new system.
4) Decouple Interstellar and interplanetary transportation systems: As you have already pointed out, your interstellar rail system uses planetoids without an atmosphere, and for safety reasons probably minimal life. By having your interstellar ships being accelerated outside of any significant gravity a lot of issues can be avoided.
5) Use gravitational lensing : both to keep track of your ships, and to fire them along different paths which result in the same destination. I was skeptical after reading another answer which had to do with using different flight paths but same origins, my issue is that laser based propulsion is like turning light into a fire-hose and using that to push something. Actually it is worse because, most of these system use a feedback system where the light is recycled or the power requirements go way up(meaning you can't use a sail, you have to have a perpendicular surface). You want the laser to push directly along the flight path. If it is hit at an angle it will start to spin. It may be possible to compensate somewhat but it is still not ideal. So how can we send multiple ships out from the same point on different paths, and have them converge at the same location? Gravitational lensing. If we find the path light is bent by the systems central star(s), you can send ships along the same flight path and the beam which is directly behind them will always perfectly aligned, because the light beam is traveling straight, it is space that is bent. Also gravitational lensing can focus a great amount of EM radiation from distant objects, making it useful for picking up the weak communications from distant ships, or observing distant planets in other systems.
6) Course corrections & Keeping your speed up: While theoretically not required, as you can send any rail-car to any location, after spending 100s of years of outside observers time maybe the receiver wants the cargo to go to another location, or the planet may have had a malfunction regarding its laser required for deceleration. It might be best to direct all traffic to the star for the system. As the train begins to make final approach (the distance to decelerate from near light speed would be 1 year if 1G is assumed) it could use the gravity well of the star to change its trajectory. Also a star is an excellent power source, if you are looking for something which must generate tremendous energy output. Also #2 (cryogenics&ridged packing-foam) I expect are quite essential if using a gravitational well for course correction. Even if people are to stay awake for most of the trip, #2 might be required during "lane-changes" or when transition to a different "leg". Where some aggressive deceleration may be expected, along with being accelerated along a new direction. If you can maintain much of your speed when transitioning to a new target, you also keep throughput up.
Just for fun: "Batteries Included" while some seem to hint that generating energies similar to what could destroy the surface of a planet every hour as not being a good idea... well here is a power proposal that makes even that look ridiculously safe! It is probably worth investigating how a large transportation hub could work. In my view it would be most ideal if the transportation hubs were situated around black holes, most ideally if the black hole was not too large (smaller the better to exploit tidal forces) and to avoid having to feed it, if it is in binary orbit around a star that would be really helpful. Such a setup would produce a vast amount of power. It is theoretically possible to produce sub-atomic black holes. Particle accelerators such as the LHC are still a couple magnitudes off what is required. Also such black holes evaporate! But still it is possible given enough energy to produce black holes, which are built in an accelerator. Now since they are produced at a high speed they are subject to time dilatation, while at rest they may only last seconds (or less) but at speeds approaching C, they can last much longer. Point of this is that a powerful accelerator which has access to massive amounts of energy (something pouring off gamma-rays seems like a good start) can store tremendous amounts of energy in black holes and ship them to planetoids in the system. Since black holes have magnetic fields see here, they can be bent and accelerated/decelerated with magnetic fields. So there is a means of capturing them and drawing off the energy (hawking radiation). As a small black hole decelerates it will produce more energy, and if accelerated less... so there is a means of controlling the output. Once the black hole starts to approach the limit where it will cease to be a black hole it should be fired back into the parent black hole... for people that thought your lasers were dangerous, having a 10000 kg black hole come apart when powering one your airless planetoid lasers would probably result in there being no planetoid!