Personally I think the biggest problem with the LHR road system in the poor signage. The poor tourists/non locals in their hire cars struggling to read those tiny little signs to the car rental places, which are located at opposite ends of the airport depending on the company, gettin in the wrong lanes then stopping in the middle of the junctions..
If the M4 spur was signed a bit better, for example have T3 in big letters over the outside lane, then T1/T2 over the middle lane, and T4 and all other areas over the inside lane, it would give drivers a mile or so to be in the right lane and would help avoid alot of the lane changing around the non-concorde roundabout and at the tunnel exit in central when people realise they are in the wrong lane once they find those tiny little signs !!.
The only new roads to be built in the last 20 years or so is down by T5, and thats not exactly complicated.
the journey off the M25 onto the M4 and into the central area is longer than the trip from Hemel
I've stopped using the M4 spur now, it is just too unpredictable, and I only have to travel a few miles to get to it. And how frustrating is it when you leave the staff car park late at night, drive down the M4 spur to be greeted by a huge traffic jam due to roadworks on the roundabout that has only just been re-built !!!. If there was some warning in the staff car parks, the staff could take alternative routes and avoid adding to the congestion !!.
That roundabout is also the source of most of the congestion with the timing of the traffic lights coming into LHR. The main block of traffic going into LHR comes down from the M4/M25 eastbound slip, yet the lights only let about 5 cars through at a time in each lane, then you have to stop again half way round whilst 1 car comes down from the M4 westbound slip !! I think it has been done on purpose to create congestion so that Mayor Ken can use it as an excuse to introduce the congestion charge around LHR as has been mooted last year.
If I were you VSlhrcsa, I'd carry on down the M25 to the next junction and go round the perimeter road, a bit longer but quicker and more reliable, or what I have also done myself, go past the M4 spur to the next junction, turn round and come back down the other way, or even go down onto the A4 from that junction and back along it - pain in the a$$ but usually quicker if the spur is solid.
