Aidan Stanger wrote:

Does TfL (or anyone else) try to estimate the value of bus lanes before
installing them? If so, what criteria do they use?

Am I right in thinking London's most expensive bus lane so far was the
one on the M4? Am I right in thinking the consensus now is that it's a
white elephant?

That's not what studies of this lanes say:

http://news.bbc.co.uk/1/hi/uk/1120542.stm

"It has now been given the government's seal of approval after a case
study showed it had cut rush-hour journey times for both cars and
buses."

AND

http://www.highways.gov.uk/roads/pro...lane/index.htm

"Conclusions
The bus lane scheme has met its primary aim set out before the scheme
was installed. The scheme has resulted in time savings during peak
periods for all types of vehicles. On average, each bus is saving 3.5
minutes and each car is saving 1 minute during each peak period.

The general public has a perception that not enough vehicles use the bus
lane. The reasons for the restriction in numbers could be included in
further publicity. The number of vehicles using the bus lane influences
the benefits of the bus lane scheme. If too many vehicles were to use
the bus lane, a bottleneck might reappear where the three lanes are
reduced to two. Therefore, large numbers of other potentially eligible
vehicle types should not be allowed to use the bus lane without careful
study."

There is also a site:
http://www.buspriority.org
which has some case studies.

I happen to know that a LONG time ago when Maggie was King that a
Minister of Transport requested an urgent review of bus lanes in London
because they apparently slowed down his ministerial car.

The person who conducted this review knew that producing the required
answer would mean rapid promotion, but his moral standing meant he
didn't fiddle the statistics and had to wait longer for a promotion.

Jim Chisholm