I think that a relatively cost effective way to alleviate some of the traffic problems on Dartmouth Road would be:

a) to put a box junction or at least a KEEP CLEAR area where it joins the South Circular to stop the blocking that currently occurs.
b) make the narrow part of the road from the SC to Derby Hill completely "No Stopping" from 7 to 10 in the morning and 4 to 7 in the evening. This will allow unimpeded flow in both directions during the busiest times and give the businesses along that stretch 6 hours during the slacker part of the day to arrange their deliveries.
c) remove all those little triangular islands outside the shops between Derby Hill and Clyde Vale and paint in some bays to maximise the available parking space.
d) If it can be done with the entrance and exit in Derby Hill then cut the pavement back outside Heron House and the Job Centre to provide a few more bays. I think it will be a bad idea both here and outside Sylvan Post if cars have to reverse onto DR to get out of the bays.
e) a zebra crossing somewhere, perhaps between say Rob's barber shop and the pools.

Of course all of our thoughts only matter if someone involved in the decision making process is taking notice of them.