humans-the coming revolution in autonomous transport has significant meaning for wildlife as well.Nature conservationists and planners need to think hard about the impact of driverless vehicles，especially in terms of the expanding of the cities.In some ways，wider developments in automotive technology are good for the environment.

　　Electric cars will increasingly replace the internal combustion engine(内燃机)，and that should，in theory，reduce carbon emissions and health­disturbing air pollution.Through minimizing traffic jams，driverless cars may also reduce energy use on the whole.Unlike human drivers，computers can avoid needless acceleration and braking that worsen jams.And，as autonomous vehicles aren't limited by human reaction times，it may make sense to increase speed limits for them on major intercity routes.So driverless cars promise a future of faster journey times with much reduced environmental impact！They may even mean less wildlife roadkill.

　　But it's the very efficiency of driverless cars that brings a challenge for planners and conservationists.The threat is an unchecked increase in low­density urbanization.Autonomous vehicles promise a future in which passengers are free to use their time productively (working，for example).And they can park themselves，which saves yet more time in the morning rush.Coupled with faster journey times，the motivation to live further out of town will increase significantly.

　　There are both push and pull factors at work here：sky­high residential prices in most cities push people away from city centres while healthy environments and green living pull people towards the countryside.The limiting factor in suburban(郊区的) spread is often travel time，either by public or private means.

　　Driverless cars completely change the situation.Existing planning policies are based on our current transport systems.Green belts，for example，are designed to reduce the expanding of the cities by restricting development within a buffer zone(缓冲地带) around an urban area.However，the reduced transport times offered by driverless cars make it easier to live outside the belt while still working inside.So these belts of green are in danger of becoming a thin layer in a sandwich of ever­spreading suburbanisation.This is，of course，a familiar challenge since the rise of the automotive age in the 1940s.However，the solutions designed by planners have been calibrated(标定) for a human­driving automotive system-not for the supercharged future of driverless transport.

Other examples of planning protection for wildlife include nature reserves，national parks and (in the UK) "Areas of Outstanding Natural Beauty".Such areas have either strict control on development，or do not permit it at all.However，they are nice places to live in or nearby.The coming revolution in automotive journey times and the ability to work behind the (computer­driven) wheel will make living in such areas increasingly compatible(可共存的) with a journey to the nearest city.