There are several areas around gloucester to go to.
First up there's the station itself with all of the usual station ammenities. From here you can see the Yard. You can also get good overhead shots from to footbridge between platforms 2 & 4.

about 4 miles south of gloucester is Haresfield. To get there from the north, take the M5 and exit at junction 12, at the top of the off ramp turn left then 1st left again to go back paralell with the M5. From the south take junction 12. At the top of the junction, go right at the roundabout to go over the M5, go straight over the next roundabout then take the first turning left.

About 1 mile you come to a T junction. Turn Right. A couple of hundred metres along there is a railway bridge.Turn right just before the bridge & the railway is on your left. ABout 1/4 mile down there is a layby next to a mobile phone mast. Park Here and walk up the short path to the crossing. Take the first right after the bridge and go to the end (outside the Beacon Inn). Here is a pedestrian level crossing on the main north/south line. to the right and left are goods loops.

Alternatively, continue past the crossing for about 3/4 mile and you will come to a farm on the right with a bridge over the railway on the left. Although the bridge is a public footpath, take some wellies as it is also the only route for the farmer to take his cows across.

Another alternative is to continue past the farm to the end of the road (another 3/4 mile). If you go right here you return to the motorway. If you go left there is another bridge ov the railway at the point where the main line at the Swindon branch split. There are no ameneities here but the town of stonehouse is about 2 miles further.