LATE last month, three Israelis who know something of what is on the mind of Ariel Sharon, the prime minister, seemed to say publicly what many others are thinking privately. Since the “disengagement” of settlers and troops from Gaza and part of the northern West Bank this summer, Mr Sharon has maintained that Israel's next territorial withdrawal will be not unilateral, as that one was, but agreed by both sides under the “road map” peace plan, which calls, eventually, for joint talks on creating a Palestinian state. But Eyal Arad, a public-relations adviser to Mr Sharon, Tzachi Hanegbi, one of his ministers, and Aharon Ze'evi-Farkash, the head of military intelligence, were all quoted as suggesting that if peace talks make no progress, Israel might stage another unilateral pullout from some of the West Bank.

Their remarks might have been trial balloons, or merely soap bubbles, but they caused instant fuss. Such a move would anger both Palestinians, who do not want Israel always setting the agenda, and many Israelis, who resent surrendering land without security promises from the Palestinians in return. Mr Sharon was quick to pooh-pooh the “rumours”. Mr Arad, for one, says he was misquoted.

But, say various sources, in high-level backroom discussions the subject is coming up time and again. “When I speak to Israelis of virtually all political stripes, they all believe it's the next thing that's going to happen,” says Robert Malley, a Washington-based analyst for the International Crisis Group, a peace-making lobby with headquarters in Brussels. There may well be no plan to do it. Yet events could inexorably lead to it. This week's murders of three Israelis by Palestinian gunmen, and Israel's response, gave a foretaste of how.

The shootings were in two different places on Route 60, the main north-south highway through the West Bank. Views vary as to which militant faction (or factions) really did it, but they may have been timed to embarrass Mahmoud Abbas, the Palestinian president, who was drumming up support on a foreign tour due to end this week in Washington. Palestinian vehicles, which bear different-coloured licence plates from Israeli ones, are subject to ever-changing restrictions on which roads they may use. Since the start of the Palestinians' second intifada (uprising) five years ago some of the main West Bank highways, as well as the by-pass roads that Israel has built over the years to connect its West Bank settlements to one another and to Israel proper, have become Israeli-only. Some, among them Route 60, are usually open to at least some Palestinian vehicles, such as trucks and public transport. But after the shootings, Israel responded by banning all Palestinian traffic from several roads, including part of Route 60.

Maariv, a daily newspaper, reports that the army has been told to start implementing a plan to make such bans permanent, though government spokesmen say there has been no final decision. Israel is at work (slowly, after foreign donors last year refused a request for funding) on building and upgrading roads, bridges and tunnels to let Palestinians travel between their towns without ever turning on to a road used by Israelis.

That will complete the division of the West Bank into two road networks (see map). Israel says this will make Palestinians' lives easier: there will be less need for checkpoints and roadblocks. Perhaps so; but the Palestinian highways will be narrower, more winding and more hilly, so trips will take longer and cost more. They also tend to go through towns instead of by-passing them, which will mean huge snarl-ups of trucks and public transport. All this will hurt the Palestinian economy.

Signs of the creeping separation have been there for a while. The UN's Office for the Co-ordination of Humanitarian Affairs has found that the number of fixed checkpoints and roadblocks in the West Bank has dropped by at least a third this year, in line with an Israeli promise in February to ease restrictions. However, that has mostly helped movement between small Palestinian villages and their nearby urban centres. The highways between the main towns, on the other hand, are increasingly lined with fences and barriers to prevent access, and there are now three times as many “flying checkpoints”, which pop up and turn back Palestinian cars at random, discouraging them from using roads that may one day become Israeli-only.

What does all this mean for the future? For two years Israel has been building a barrier through the West Bank—for security, say the Israelis. It mostly hugs the pre-1967 border (the Green Line), but bites off the areas with the biggest settlements too, taking about 10% of the Palestinians' West Bank territory. The ugly barrier, reminiscent in places of the Berlin Wall (about 7% of it so far consists of nine-metre high concrete slabs), has attracted international condemnation. But the common assumption is that it is intended to be an eventual international border and that the Jewish settlements on the Palestinian side, with some 70,000 residents, will be evacuated in a peace deal, along the lines apparently on offer by Israel at Camp David in 2000.

Yet Israel need be in no hurry. Though less visible, and almost ignored amid the international outrage, the dual road system is much like the barrier. It cuts settlers off from Palestinians, making them safer from attack and securing settlements deep inside the West Bank, not just those close to the Green Line. As with the barrier, each terrorist attack will not only further postpone the peace process—Israel says there can be no progress until the Palestinian Authority (PA) meets its road-map obligation to disarm militants—but will reinforce the argument for keeping the system in place.

Meanwhile, if the peace process remains stuck, it is not hard to see how Israel might stage another unilateral pullout. Since the success of the Gaza disengagement, Israeli support for another such move, though still in the minority, has increased, according to Tel Aviv University's monthly Peace Index poll. An early draft of the disengagement plan included about a dozen more settlements in the middle of the West Bank, which in the end were left intact. A few other isolated settlements are now lobbying the government to be relocated into Israel. Any of these could, in time, become the focus of Israel's next unilateral withdrawal. And that, argues Mr Malley, could serve both Israeli and PA interests. Israel would give up strategically inconvenient outposts while saying, once again, that it is making concessions to the Palestinians. The PA would, once again, make political capital out of Israel's withdrawal, without the humiliation of having given its consent to an unfair deal.

But terrorist attacks would continue to kill Israelis. The West Bank's balkanisation would continue to impoverish Palestinians. Israeli settlement-building would make a viable Palestinian state ever harder to achieve: this summer Israel, ignoring its own road-map obligations, announced plans to increase the number of settlers in the Jordan Valley, in the east of the West Bank, by 50% in one year. It is still building hundreds of dwellings a year in other settlements too.

Israeli strategists these days tend to see the Jordan Valley not as an essential “security buffer”, but as a large bargaining chip. Populating settlements will give them more weight in any future negotiations. There are already nine times as many settlers east of the barrier as the number evacuated from Gaza, and they include the most hardline ideologues. If enough time goes by, the Palestinians may have little choice but to accept a Swiss-cheese state, comprising most of the West Bank but riddled with settlements, in which travel is severely hampered. And in the worst case, if there are no peace talks, the dual road network lets Israel contemplate pulling out from up to 40% or 50% of the West Bank's territory unilaterally, while keeping most of its settlements.

What might stem this grim onward march? The PA's most effective weapon would be incontrovertible signs that it is bringing violence under control. Mr Abbas's slow progress on this score has been hampered by PA infighting, his own weakness as a leader (though polls show he is growing more popular), and the fact that the PA forces still cannot operate in Israeli-controlled areas of the West Bank. And since Israel, not surprisingly, responds to attacks by clamping down, as it did this week, each attack makes the job harder—and strengthens Israel's determination to keep its systems of separation.