You may feel a sense of dread on the road these days, watching other drivers gab on phones and fiddle with iPods. But by one measure, American motorists are safer than they've been in decades -- though it's not clear exactly why.

    The rate of fatalities per 100 million miles of vehicle travel on U.S. roads is at its lowest since the government began keeping such data in the mid-1970s, according to the National Highway Transportation Safety Administration. The NHTSA's recent projected decline in overall traffic deaths for the first half of 2009 was played as a 'silver lining' to the lousy economy: Fewer people driving to work, fewer people dying on the road.

    That could be true. The raw number of highway deaths tends to drop during recessions, according to government figures.

    But more significant is the decline in the death rate, or deaths spread across miles of driving -- long division that helps smooth out effects of economic cycles. Based on the latest estimates, there were 1.19 deaths for every 100 million vehicle miles traveled in the second quarter of 2009. That compares with an estimated rate of 1.1 for the first quarter.

    By comparison, the deaths-over-miles-traveled ratio was 1.46 for all of 2005 -- a year in which 43,510 people died on the roads. If current trends continue, it's possible that fewer than 35,000 people will die on U.S. highways this year.

    'We are hitting fatality rate levels we couldn't have imagined a decade ago,' says NHTSA spokesman Rae Tyson.

    Exactly why driving is less deadly isn't clear, though the trend has been going on for several years. The data don't explain the cause of every accident nor why accidents that could have been deadly weren't.

    One factor may be better safety technology. A decade ago, 77% of vehicles sold had no side airbags, according to Insurance Institute for Highway Safety data. In 2009, only 10.3% of cars didn't offer side airbags -- and nearly 65% did offer head- and torso-protecting airbags as standard equipment.

    Electronic stability control -- systems that use the car's brakes to prevent skids -- were available on just 9% of vehicles sold in the U.S. in 1999. For 2009, 74% of cars and 100% of sport-utility vehicles sold offered the technology as standard equipment, and 85% of vehicles sold overall offered it as either a standard or optional feature.

    Highways also have more safety features. Rumble strips, which alert drowsy drivers when they are drifting off the pavement, are more common, as are barriers that prevent vehicles from sliding across medians of divided highways.

    And believe it or not, drivers are behaving better, too. More U.S. motorists than ever are wearing seat belts -- 84% by the most recent government estimates, up from about 60% in the mid-1990s. 'Click It or Ticket' campaigns annoy some people, but they also apparently have motivated many seatbelt-averse people to change their ways. Tougher speed enforcement and campaigns against drinking and driving could be holding the fatality rate down as well.

    如今開車行駛在路上，看到其他司機對著手機喋喋不休或者是擺弄手里的iPod,你或許會感到一絲不安。不過從某一個方面來看，美國司機的駕駛安全系數卻是數十年來最高的──盡管個中緣由還不是很清楚。

    美國國家高速公路安全管理局（National Highway Transportation Safety Administration）的數據表明，自上世紀70年代中期有數據記錄以來，美國每1億英里駕駛里程的事故死亡人數目前處于最低的水平上。高速公路安全管理局最近發布了2009年上半年交通事故死亡總數預計將出現下降的消息，這不啻于經濟陰霾下的"一絲光亮":開車上班的人少了，因此交通事故喪生的人也少了。

    這種說法可能沒錯。美國政府的數據表示，高速公路死亡人數在經濟衰退期間有下降的趨勢。

    不過，死亡率的下降，也就是按英里數計算的死亡人數的下降更為重要，因為這種計算方法有助于消除經濟周期的影響。根據最新的預測數據，在2009年第二季度，每1億英里駕駛里程的死亡人數為1.19人，而在第一季度，這個數字為1.1人。

    與之相比，2005年全年的英里駕駛里程死亡人數為1.46人──當年共有43,510人死于車禍。如果目前的這種趨勢能夠繼續保持，那么今年高速公路死亡人數有望少于3.5萬人。

    高速公路安全管理局的發言人泰森（Rae Tyson）表示，我們正在接近的這一交通事故死亡比率在十年前是無法想象的。

    至于駕駛安全為什么會提高，沒有人能夠說得清，盡管這一趨勢已經持續了數年之久。從美國政府的這一數據沒有提供交通事故的原因，以及為什么從前可能致死的事故如今卻沒有那么可怕。

    一個原因或許是更先進的安全科技。美國高速公路安全保險協會（Insurance Institute for Highway Safety）的數據顯示，十年前，在美國銷售的車輛中有77%沒有安裝側氣囊。而在2009年，只有10.3%的汽車沒有配置側氣囊；而近乎65%的汽車將頭部氣囊和軀體固定氣囊列為標準配置。

    安裝了電子穩定控制系統的汽車在1999年時僅占在美銷售車輛的9%.而在2009年，在美銷售的74%的轎車和全部運動型多功能轎車（SUV）將這一技術作為標準配置；而在美銷售的所有車輛中，有85%將電子穩定控制系統作為標準配置或選擇性配置。電子穩定控制系統能夠利用汽車的剎車裝置防止打滑。

    高速公路也安裝了更多的安全設施。振動帶以及隔離帶都更為普及。振動帶能夠在困倦的司機偏離車道時起到提醒的作用，而隔離帶能夠防止汽車越線開向逆行車道。

    另外，不論你是否相信，司機們的表現也更好了。在美國，系安全帶的司機人數達到了前所未有的水平──最新的政府估算數據顯示，有84%的司機系上了安全帶，這比上世紀90年代中期的60%增加了不少。在美國發起的"系安全帶，還是吃罰單"運動惹惱了一些人，不過這也讓許多不愿系安全帶的人改變了他們的作法。更為嚴格的限速措施和針對酒后駕車發起的一系列整治措施也對車禍死亡人數起到了抑制作用。