Go to almost any rail-based retail strip in Melbourne and you'll find a 'good side' and a 'blighted side'.
The good side has the busy shops; the bad side has the empty shops, derelict buildings, tattoo parlours, pawnbrokers, sex shops, secondhand dealers and other low-rent and marginal uses.
The reason is visibility and pedestrian access. A thriving retail shopping strip caters to many needs and tastes. You won't want to go into every shop, but if there's one across the road that grabs you, one expects to be able to walk directly to it and be inside within 20 or 30 seconds. Poor visibility, waiting or backtracking kills the shopping experience and reduces customer count and sales. This is because the number of shops one can impulsively entered in a 30 minute visit to the strip is reduced. If people can't get adequate and accessible variety they they'll go elsewhere (eg a large shopping centre where the traffic problems are left outside in the car park).
This goes some way to explain why shopping strips based around or near traffic sewers (North Road Ormond or South Road Moorabbin) are failures, while those based around smaller streets (Puckle Street Moonee Ponds or Koornang Road Carnegie) are successes. And along the same street, eg High Street Preston, those sections with closer intervals between pedestrian signals win more shoppers than those that don't.
Nevertheless traffic along a shopping street (or more precisely long gaps between pedestrian crossings and long cycles for those that exist) isn't the only enemy of easy access to shops. Railway lines or major highways, running across a shopping street can divide an area, reducing visibility and/or access. Shops require much closer links between them than do houses; customers often go from shop to shop, but people seldom go from house to house in a street. Not only does visibility have to be good, but retail shops need to be almost adjoining and on the same level to maintain interest and encourage the shopper to 'drop in'.
Anything like a major highway or railway line violates the need for good sight and quick access and condemns the less favoured half of the shopping strip to decline (*). An underpass helps, but not if it is indirect and results in extra walking (as many low-grade DDA-compliant ones can be). Overpasses have similar problems. Even the 'cage' appearance of at-grade gates or booms reduces sightlines, even though in 80% of cases these won't be closed and access is faster than the perception of same.
What about grade seperation of road and rail? Local retailers appear to like this and think it will fix all their problems. While there may be other benefits of grade seperation, fixing a divided retail strip is not necessarily one of them. Indeed it could make matters worse; making a two dimensional problem into a three dimensional problem, further 'killing off' the less favoured side.
Oakleigh, Huntingdale, Sunshine and Richmond station grade seperations are all failures from an urban amenity standpoint. All have caused or encouraged significant urban blight in the overpasses' shadow. Even Elsternwick, which I have praised before, has it's 'bad side' of the line, as Reuben points out (and it was that post which encouraged this one).
If grade seperations aren't the cure for divided shopping strips, what is? I don't think there is one given the clear sightlines and continuous access required within a shopping strip for it to function as a whole. In this case it might be better to admit defeat and rezone the 'blighted sides' of shopping strips from 'retail' to 'residential - high density' with mixed uses also permitted.
This has a number of benefits. For a start it increases the pedshed of the railway station and local shopping strip, generating custom for both. While residents of this area will need to cross the railway or road to reach the shops this is acceptable since once over the line access between all shops in the strip will be good. Urban blight will be minimised since the retail strip will no longer be divided and there will be increased pedestrian traffic from local residents. And if the strip needs to be expanded, some houses could be rezoned mixed use or commercial towards the unblocked end of the strip.
(*) Reservoir seems to be one exception - with two active shopping strips on both sides of the railway.
