For the thousands of Palestinians who travel daily between the north and south West Bank, there is only one route: a steep and narrow track up and down a canyon with 15 hairpin turns and the scars of frequent accidents.

Wadi Nar means "the Valley of Fire," a place where brakes fail, clutches burn up, engines stall and people die.

The ride up and down the canyon walls is among the worst routes Palestinian motorists must use to circumnavigate the towns, army posts and well-maintained highways built for Israelis on land the Palestinians claim for a future state.

West Bank Palestinians are barred from most of these areas. Israel says the system is meant to reduce friction and fire-fights between Palestinians and Israeli settlers. Israel's critics say it benefits 300,000 Jewish settlers while pushing 2.3 million Palestinians onto longer, bumpier alternatives, as well as carving up the territory in ways that complicate future statehood.

The Israeli establishment itself is divided over the extent of the separation. Last month the Israeli Supreme Court overrode the military's objections and ordered it to let Palestinians use part of a major highway previously open only to Israelis.

Meanwhile, as Arab-Israeli violence has declined, many roadblocks and checkpoints have been lifted and even Wadi Nar's worst stretch is getting improvements from a U.S.-funded building project.

But the critics say the latest opening only partially improves life for Palestinian motorists, and that overall the road-building policy is discriminatory.

Palestinians say the back routes do more than fray nerves — they delay and wear out vehicles, the West Bank's sole means of delivering goods and commuters, and further drain an economy struggling to recover from decades of conflict.

No road burns out more cars than the Valley of Fire.

"All of Wadi Nar is one huge hill going down and one huge hill going up, so it kills cars," said Albert Giacaman, whose company in the southern city of Bethlehem supplies office equipment to schools and offices throughout the West Bank.

To reach northern clients, Giacaman's cars cross the canyon 40 times a week. Maintenance is costly and he has to replace the fleet every four years instead of eight, he said.

Wadi Nar is the worst, said Raed Qais, one of Giacaman's drivers, setting out on one of his 10 weekly trips though the canyon.

First his route twists through three villages and over a dozen speed bumps on a road that doesn't look like what it is: a major thoroughfare.

Then the two-lane road zigzags down the canyon between a wall of rock and a thin fence on the edge of a cliff. There's no median, garbage litters the shoulders, and holes in the fence mark crash sites.

Qais pointed to where he saw a truck hit the wall. Later, he showed where a minibus hit a truck head on, killing seven people.

He said he sees an accident about every 10 days, more in rainy winter.

Suleiman Abdallah, mayor of a nearby village, said he has seen minibuses swerve around slow cars and crash into oncoming traffic. Sometimes loads slip off trucks, blocking the road.

At the valley floor, Qais crossed a bridge over a sewage canal. His engine roared as he started the climb, passing a work crew on the USAID-funded project to repave and add safety features to the road's worst stretch. After five more tight curves, he reached an Israeli checkpoint manned by two soldiers and prepared to wait, but on this day traffic was moving along and he was waved through with a glance.

Qais would gladly take another road — but there isn't one.

There used to be. Twenty years ago, Wadi Nar was a dirt farm road, and Palestinians driving between north and south went through Jerusalem. But then Israel barred entry to West Bank cars, forcing them to use back roads around the city.

After the Palestinian uprising broke out in 2000 and Israeli cars came under fire, Israel opted for separation. It banned Israelis, whose cars have yellow license plates, from entering Palestinian areas, and built a vast network of bypasses and barriers, hemming in the green-plated Palestinian traffic.

In some areas, it built roads to link Palestinian communities, some passing through tunnels under highways. But in most places, Palestinians had to find their own detours. Wadi Nar is one.

As violence has declined, Israel has eased movement between Palestinian cities and allowed Palestinian cars onto many formerly segregated highways.

Some remain off-limits. The 14-kilometer (9-mile) road between the Elon Moreh settlement and the highway is for Israelis only. Some 16,000 Palestinians living nearby must take a detour that can make their journey four times longer.

But even shared roads tend to favor the settlements because Palestinian communities often lack access roads. "When balancing Israeli and Palestinian interests ... the authorities very often choose the Israeli interests," said Sarit Michaeli of B'Tselem, an Israeli human rights group.

Israeli government spokesman Mark Regev said Palestinians should blame those who attacked Israelis. "The Israeli government is committed to making sure that on one hand there is maximum movement and access, and on the other hand that security is maintained for Israelis and Palestinians alike," he said.

A drive on two overlapping routes shows who benefits most.

Palestinian tax official Mohammed Taha used to drive 17 kilometers (10 miles) to his job. But a closure on that road doubles his journey, taking him around two settlements and through a tunnel under a settlement access road.

All Palestinians from nearby villages use the same detour to reach their regional hub, where many work and all must go to visit a bank or a hospital, Taha said.

A few hours later, Jewish settler Adi Itskovitch, 42, stopped the van carrying his wife and seven of his 10 kids on the road over the tunnel Taha uses to get work.

The well-groomed road, parts of its 30 kilometers (18 miles) divided by flower-filled islands, later expands to a four-lane highway that speeds cars from the central West Bank into Israel in about 20 minutes.

Some seven kilometers (four miles) of it is closed to Palestinian cars. But for Itskovitch, it makes commuting a pleasure.

"It's a very good road," he said, firing the ignition. "We love it."