Do you really think people will not run or cycle along the river path because of a bus on a small bridge?
No, of course not, but the crucial link across the river will become irrepairably reduced, possibly to the point where it is effectively unusable.
It isn't a big bridge, I doubt there is room for busses/guided tramways and non-motorised traffic side by side. So what we'll get is a u-turn on any assurances of continued access, or some hopeless traffic-light scheme. All, I'm sure, badly handled by Bristol City Council, renowned for awful project management and craven capitulation to the demands of any and every commerical operator. See FirstBus.
This is the only traffic-free route into the city from the south west. The scheme, quite apart from the bridge issue, is poorly conceived, expensive, and threatens to wreck a whole lot of good stuff.
This is speaking as someone who lives in Long Ashton, and would quite like to be able to get the 4 miles into the City Centre in under an hour during rush hour. Luckily for me, I'm able bodied and can ride a bike.
I'm also not sure why they're replacing a perfectly good Park & Ride.
If they put a bit of thought into the Park & Ride scheme, it would be much better. Only that is less exciting and makes less profits for all involved. It could also impinge on road space, which would elicit howls of protest, and require some political courage.