KOBILJACA, Bosnia-Herzegovina (AP) _ In a scene unthinkable just weeks ago, traffic chaos reigns here.

A British NATO tank, its tracks clattering on sheet ice, tried to haul a French armored car out of a ditch. Bosnian cars, back on the road after 3 1/2 years of war and ill-equipped for winter, tried to slalom around the hapless NATO vehicles but ended up in a fender-bending concertina.

The jam might be bad news for travelers trying to pass Kobiljaca, just west of Sarajevo. But it's good news for NATO.

Roads, and who travels along them, are a barometer of Bosnia's stop-go moves toward peace. More traffic means more confidence among Bosnians that war is over and it is safer to move around.

So far the alliance has largely succeeded in getting freedom of movement _ a cornerstone of Bosnia's peace deal signed Dec. 14 in Paris _ off the paper and onto the streets.

But informal checkpoints still exist, particularly on territory where nationalist tensions run high, and there most Bosnians cannot pass.

``We feel there is improved freedom of movement in most areas of this region,'' said Cmdr. Mark van Dyke, spokesman for the 60,000-strong NATO Implementation Force.

``In some areas we have complete freedom of movement, in other areas it may be less,'' he said, adding he knew of ``checkpoints that pop up and vanish'' depending on whether NATO troops are around or not.

In a tense confrontation with NATO earlier this month, Serbs released 16 Muslims detained while passing through the western Sarajevo suburb of Ilidza. They were charged with ``spying.'' But that isn't stopping other Muslims and Croats from passing through the Serb-held suburb.

Zulfo Muratovic, a Muslim driver with Sarajevo's Centrotrans bus company, said Serbs throw rocks at his bus when he passes Ilidza.

But that's better than the anti-aircraft gunfire he used to face on the perilous Mt. Igman route, previously the only road in and out of Sarajevo.

``Through Ilidza, it's scary but short,'' he said. Since NATO arrived, he has slashed journey times across Bosnia by hours.

Before, ``you would just set off and drive and drive until you got there, sometimes not even the same day you left,'' he said.

It is easy to check on who is venturing where, because in Bosnia even cars are identified ethnically.

Bosnian Croats issue plates with Croatia's red-white checkerboard emblem. Serb plates are written in Cyrillic, and cars of Muslims and others loyal to the Bosnian government bear Bosnia's fleur-de-lis shield.

In Kobiljaca, things are definitely improving.

For most of the war, Serbs sealed their siege of Sarajevo by closing the main route to the Adriatic coast. Nobody could pass except vehicles under U.N. escort.

Now, Croat-plated cars from central Bosnia are bumper-to-bumper with buses from Sarajevo, and trucks from Valjevo, in the heart of Serbia.

Most common are Serb residents of Sarajevo, their cars towing trailers of possessions out of the region.

Sarajevo's Serbs say they prefer to leave rather than stay to see the capital reunited March 19 under their war-time enemy, the Muslim-led government, and many fear revenge attacks.

``Revenge? No, now is the time for peace,'' said Petar Kovac, a Croat gas pump attendant in the central, Muslim-governed city of Travnik. He said traffic had doubled through Travnik since the treaty signing.

But NATO's task _ ``to lay a carpet of stability and normality and confidence around the country,'' according to NATO spokesman Brig. Gen. Andrew Cumming _ is far from completed.

In central, Croat-held Jajce, two heavily manned checkpoints guard the town's main approaches. Muslims may only pass in convoys with Croat police escort, and Croat militiamen rule arbitrarily if foreign reporters may pass or not.

Further on, reporters traveling the NATO-patrolled route from Jajce to the northern Serb stronghold of Banja Luka are waved through once-impassable Serb territory by scrupulously polite policemen. But no Croats or Muslims dare venture into the zone.

To alleviate tensions, at least between Muslims and Croats who were handed 51 percent of Bosnia in the peace accord, plans are being made to swap the ``ethnic'' plates on Bosnian cars for plain plates. This way, the car's origin and the ethnicity of its driver is not immediately obvious.

Brig. Richard Dannat, commander of British NATO forces near Jajce, said local animosities and fears have frequently confounded NATO's attempts to open up roads for all.

``I sometimes think every Bosnian's dream is to own his own checkpoint,'' he said.