my 2 cents...

护路
* 1. patrol and guard a road or railway
* 2. road maintenance
i.e.
A worker employed to maintain or inspect railroad tracks.
巡道工，护路员受雇保养或巡查铁道的工人

保交
Intersection Preserving / Preserving Intersections
i.e.
THE SURJECTION WITH UNION AND INTERSECTION PRESERVING BETWEEN COMPLETE LATTICES
完备格间的保交并映射

combined:
intersection preserving and road maintenance
or
preserving intersections and maintaining roads

“’编精编实编强防卫作战队伍和保交护路队伍。结合我镇战时主要担负地面防卫、动员支前、保交护路的任务，严格按编选配人员，着力提高专业对口率和作战能力。”

”去年5月，军分区根据战时可能担负的动员支前任务，明确高速公路沿线10多个乡镇均要成立保交护路民兵大队。任务下达后，所有乡镇的党委书记亲自挂帅筹集资金、购买装备、挑选兵员，不到一个月，10多支保交护路民兵大队全部组建完毕。”

“先后圆满完成了省军区、军分区党委赋予的省民兵政治教育改革试点座谈会、省正规化管理现场会、保交护路等大项军事任务。”

“先后有防化救援、医疗救护、保交护路等分队都服务于经济建设的主战场。”

”... 支前、保交护路和防卫作战三大任务，也就是“兵要补得上，物要供得足，路要保通畅，..."

"提高指挥控制、防卫作战、保交护路、动员支前、综合保障的能力。"

"包括保交护路、物资供应、技术保障、科技信息支前和其它战场勤务。"

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Note added at 14 hrs (2008-06-25 05:16:08 GMT)
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‘But the climax of the show was the anti-terror drills.
In one, security forces dressed up as a road maintenance crew and hid in rubbish bins, popping up in time to intercept a hijacked bus.’（Google)
-> security drills (a total guess)

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Note added at 14 hrs (2008-06-25 05:17:13 GMT)
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http://www.stuff.co.nz/4502377a12.html

I guess this is some kind of promise or resolution made by a government in order to "guarantee smooth traffic flow" in the city instead of protecting the road. And "护路" should be a repetition of "保交" just for the purpose of emphasis or speech rhythm in Chinese.
FYI.