If speed limits are reduced...

Petroleum consumption is reduced because cars use less fuel per kilometre travelled; general air pollution is reduced for the same reason.
Fewer pedestrians and cyclists are killed or injured.
Fewer motorists are killed or injured.
Cycling becomes safer and more pleasant, and more people cycle.
Walking becomes safer and more pleasant, and more people walk.
Travel by train becomes more competitive and more attractive.
Vehicle noise is much less at low speeds, so noise is reduced improving city environments and allowing those who live there to be happier.
Driving is less stressful.
It becomes impractical to travel quite such long distances as we used to.

If petroleum consumption is reduced...

Western nations have less reliance on unstable and undemocratic petroleum producing nations.
Less greenhouse CO2 is produced.
General air pollution is reduced, improving health.
The limited remaining stocks of petroleum will last longer.
The balance of trade for petroleum importing nations improves.

When people see others cycling, they are more likely to cycle themselves.
Fewer people drive.
Governments have a bigger incentive to build bicycle paths, making cycling safer.
Physical fitness is increased.
Obesity is reduced and health is improved.
People will save money.

If people see others walking, they are more likely to walk themselves.
Less people drive.
Governments have a bigger incentive to improve walking paths, making walking more pleasant and safer.
Physical fitness is increased.
Obesity is reduced and health is improved.
People will save money.

Fewer people drive.
The more people who travel by train rather than by car, the less petroleum is consumed, the less general air pollution there is and road congestion is reduced.
Obesity will be reduced because people will have to walk more to and from train stations.

There is less need to build expensive new roads.
Those who stop driving have less cause for stress, resulting in greater happiness.
Congestion on roads is reduced and that reduces stress in those who continue to drive.
Less road users will be killed and injured.
Petroleum consumption is reduced because other methods of travel consume less petroleum.
Less greenhouse CO2 is produced.
General air pollution is reduced.

It provokes less terrorists and then it has less reason to fear terrorism.
'Defence' costs are reduced, the money saved can be spent elsewhere.
Its citizens can have more respect for the increased ethical standards of their government.
Its leaders can have more self respect.
It improves its standing among other nations.
There is more peace in the world.
People like me are less likely to criticize it on the Net.

Their quality of life improves.
Their medical and hospital expenses are reduced and they have more to spend on other things.
They will be better able to walk and cycle.
They will be happier.

Human suffering is decreased, happiness increased.
More people will be able to do valuable work and fewer will need to rely on disability pensions; the economy will be improved.
The nation's health costs are decreased and the money saved can be spent elsewhere.