Policy instruments (1) - Transport Policy and Planning in Great Britain - page 191

The general highway network
Public highway authorities own and manage the general highway network because, in
the absence of a national system of electronic charging, it is not practicable for the costs
of investment to be recouped directly from its users. (To prevent 'free-riders' it would
be necessary to install toll-booths at the end of virtually every street!) Nevertheless,
as far as investment in new or improved roads is concerned, public investment is still
directed as if individual motorists paid tolls for each journey they made, using the
evidence from cost-benefit analyses (12.7).
Given the existence of an ordinary highway network which provides for general
mobility it is however feasible to consider the provision of new or improved facilities
on a separate basis (i.e. where they offer additional opportunities) and for the associated
investment to be recouped by tolls from motorists on the routes concerned. (In effect this
follows the practice established in the 18th century with the building of turnpike roads.)
This is economically feasible in the case of inter-urban motorways (as in France and
Italy for example) and has been adopted in England with the Midland Expressway (the
M6 relief road north of Birmingham opened in 2003). The idea has also been explored
of tolling additional lanes as part of widening schemes for motorways such as the M25.
In the British context the combination of the density of the existing main road
network and the relatively short distance of many motorised trips means that there
are relatively few opportunities for new roads or lanes which it would be practicable
and commercially viable to operate on a tolled basis. (The extension of the M6 relief
road northwards towards Manchester was one such possibility recently studied.)
Commercially the best prospects arise in situations where traffic demand is sufficiently
high that conditions on the existing (nominally 'relieved' road) remain congested -
as in Birmingham - so that there is a strong incentive for its users to switch to the
alternative, tolled route. However given motorists' antipathy towards congestion and
the high levels of motoring taxation they incur already this is not a very attractive
feature to emphasise as a matter of public policy!
This dilemma can be overcome in the special circumstances of river or estuary
crossings where a toll has been applied from the outset on the original bridge or
tunnel. In the case of the 'second' Severn Bridge and Thames crossing at Dartford
an additional facility has been provided as a private venture but with the consortium
also assuming the debt (and taking the tolls) of the original bridge/tunnel. The pair
of crossings are then operated 'as one' (in fact one in each direction) so that the
imbalance in conditions between one tolled and one untolled facility does not arise.
Capturing additional benefits
With toll roads and any other transport facility for which users are charged, the bulk
of user benefits are expected to be recouped through charges or fares leaving the case
for public investment to depend primarily on non-user benefits. With the general road
network however non-user benefits are additional to the benefits received by motorists
noted above which normally provide the main justification for investment.
The context in which the possibility of public investment arises differs as between
private and publicly owned facilities. Private companies have their own sources of
capital whereas public agencies are mostly dependent on central government. A
company will have to satisfy its investors on the financial return it expects to obtain,
but how it does this is a matter for private negotiation. As a general principle the gains