You are right. It is a complex matter and it is likely any solution will upset some but be good for others. The key is to get the balance right so that any money spent can benefit many people. It is hard to critique the current proposal as there hasn’t been a lot of detail. The obvious thing that needs clarification is regarding the imposition of one-way traffic for the top. Is it permanent or just for the 2 hours as @robin.orton and most seem to have assumed? I am going to take it that it is temporary but it is a very critical thing to be ambiguous. These are personal opinions. It is a long read so feel free to skip to the options and table at the end.
Safety, I have children, double parking, driving on the wrong side to pass a double parked car are all major hazards for kids. I think one way traffic is a way to make this easier and more predictable for children. I think the current envisaged plan is counter-productive. A child has to look one way before 9:15 but afterwards must look both ways, many will forget. A child has to look one way on the top of the road but then when they pass an invisible border they must look both ways, many will forget. My simple view here is that you have one rule on which way the traffic flows on one road and not three rules over two parts of the same road.
Congestion/Pollution, the main pollution point in my opinion is the bottleneck between the bottom of Thorpewood Avenue from Derby Hill Crescent exiting to Dartmouth Road. Yes, Eliot Bank has it bad on school days for an hour but this junction has it bad on school days and in the evenings and weekends with Pools traffic, not so much with the Pools closed but it is likely to get worse especially with the Pools reopening and The Bridge being closed. My view here is that making this section one way would reduce congestion. The downside is this might speed up traffic and create longer journeys for residents which would be very unpopular.
Parking, a CPZ is probably the obvious and best answer but it is hard to make the case now in these troubled times. A one-way down street to make it more difficult and time consuming for short term parking with no entrance on Dartmouth Road would probably make the Sainsburys and station back car park more attractive. This would have the benefit that it would add more footfall to London Road and DR shops and cafes. Parking there is free for 2 hours.
Driveway Protection or how do you stop people parking over driveways. A CPZ is the council’s recommendation in this case but this will suffer from the fact the council can’t be bothered to enforce parking. Cameras blocking all traffic on a road between the times of congestion is the most effective solution for this.
Fairness/Equality of opportunity. Any scheme must be seen to be benefitting the many rather than the few. It can’t be seen as shifting the problem down the road. The compromised/half school street is seen as benefiting around 50 households and a few hundred children while making it worse for hundreds of households and up to a thousand children. The original school street for the whole of Thorpewood Avenue which sought to include both schools and all roads below Radlett would be seen as a simple, one road, one rule, benefiting over 600 children and a few hundred households. It would effectively be a neighbourhood scheme rather than a section of a street scheme. There would be overflow onto Kirkdale with the need to probably put a pedestrian crossing there as well as some other measures. I don’t think @marymck would be happy but it would be good to work with these residents/schools as I get the impression they currently feel ignored.
Driving Parents, the encourageable ones have changed, the rest can only be changed if life is made difficult for them except those parents and children with mobility issues who need their access rights maintained. The all street school street or a CPZ are probably the best solutions.
Cost Benefit Analysis. If this was work, my boss would ask me which is the cheapest, which has the highest risk, which is going to reach/benefit the most people at the least cost and the final one which is rarely chosen, the most costly one. I have detailed the options below.
Options:
Cheapest: One way down (eastbound) Thorpewood Avenue. Safety, clear one rule one street permanent not changing twice daily. It should lower congestion but might speed up traffic. Probably the most unpopular with residents. In these times with little money available, it might be the best thing to do.
Highest Cost per person: Small/half school street, will deliver protected driveways but will risk alienating a lot of other residents/children who will experience more pollution and congestion. It is not clear whether it will benefit EB kids walking to school if it just moves pollution. Safety aspects seem confusing.
Lowest Cost per person: An all Thorpewood School street would be seen as a neighbourhood scheme with the lowest cost per person who benefits as it would include both schools, multiple streets and all the people who down TA. It would probably need the introduction of one way traffic to TA permanently. Costs one camera more than the small school street.
Most Expensive: A CPZ would be directly paid for by the residents whereas all the other schemes are free/indirect payment. It would be hard to convince the residents to pay money for the sake of the common good as @robin.orton said but is probably the best option.
I have put in simple table below which I would have preferred to colour in or use traffic lights but you can take it that Good is Green, Good And Bad is amber and Bad is Red. I am happy to let someone colour this in. It is obviously my personal opinion so feel free to disagree but as it is half term you may not get a prompt response. It doesn’t cover all options but perhaps we could get a few more and put them to a vote. Voting won’t change anything as this is Lewisham 
| Factor |
One Way |
Half School Street |
School Street |
CPZ |
| Safety |
Good |
Good & Bad |
Good |
Good |
| Congestion |
Good |
Good & Bad |
Good |
Good |
| Pollution |
Good & Bad |
Good & Bad |
Good & Bad |
Good |
| Parking |
Good & Bad |
Good & Bad |
Good & Bad |
Good |
| Driveway |
Bad |
Good |
Good |
Good |
| Fairness |
Good |
Bad |
Good |
Good & Bad |
| Simplicity |
Good |
Bad |
Good |
Good |
| Parents |
Good |
Good & Bad |
Good |
Good |
