证据优于意识形态：伦敦低交通街区与全面20英里/小时限速制度的量化评估
Evidence Over Ideology: A Quantitative Assessment of LTNs and Blanket 20 mph Regimes in London
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中文总结 AI 辅助
本研究量化评估伦敦低交通街区和全面20英里/小时限速，发现经均值回归校正后安全收益甚微，且限速标志无法自我执行，建议转向有针对性的物理工程措施。
中文摘要 AI 辅助
我们利用2020至2024年的伤害碰撞记录，评估了伦敦低交通街区（LTNs）和全面20英里/小时限速对道路安全的影响。由于伦敦主要通过仅设置标志的命令而非物理交通稳静化措施来实施20英里/小时限速，本研究评估的是全面法定模式，而非原则上较低的城市限速。对于低交通街区，我们应用了一个因果分析流程，结合了朴素的干预前后比较、用于均值回归（RTM）的经验贝叶斯收缩以及空间双重差分法。朴素比较表明碰撞大幅减少，但经验贝叶斯调整显示，其中很大一部分反映了均值回归。经过校正后，仅有一个区域显示出统计显著的内部区域减少。我们未发现边界道路碰撞转移的一致证据，也未发现内部安全改善的一致证据。鉴于校正后的收益有限，边界道路上每辆车约10秒的小幅行程时间增加，在货币价值上抵消了安全收益。对于20英里/小时与30英里/小时道路的比较，在14种情境下使用五种关联性方法显示，致命或严重（KSI）碰撞比例的总体差异可忽略不计（0.6个百分点）。在控制错误发现率后，有四种情境显示20英里/小时道路上的KSI比例稳健地更高：A级道路、交叉口、人行横道和单车道道路，且没有任何情境显示稳健的降低。在道路几何特征提示更高车速的交通走廊中，仅设置标志的限速无法自我执行。这些发现突显了一个结构性的“错误道路问题”。不加区分的仅设置标志的限速带来了经济负担，却未带来相应的安全回报。交通管理部门应放弃全面的法定默认限速，转而回归在高危害走廊上采取有针对性的物理工程措施。
英文摘要
We evaluate the road safety implications of Low Traffic Neighbourhoods (LTNs) and blanket 20 mph speed limits in London using injury-collision records (2020-2024). Because London implemented 20 mph limits primarily via sign-only orders without physical traffic calming, this work evaluates the blanket statutory model rather than lower urban speeds in principle. For LTNs, we apply a causal pipeline combining naive pre/post comparisons, Empirical Bayes shrinkage for Regression to the Mean (RTM), and spatial Difference-in-Differences. Naive comparisons suggest substantial crash reductions, but Empirical Bayes adjustment reveals much of this reflects mean reversion. After correction, only one zone exhibits a statistically significant inside-area reduction. We find no consistent evidence of boundary-road crash displacement nor uniform inside safety gains. Given the modest corrected benefits, small journey-time increases on boundary roads (approximately 10 seconds per vehicle) monetarily negate safety gains. For 20 mph versus 30 mph roads, five associational methods across 14 contexts show that the aggregate difference in the fatal or serious (KSI) collision share is negligible (0.6 percentage points). Controlling the false discovery rate, four contexts display robustly higher KSI shares on 20 mph roads: A-roads, junctions, pedestrian crossings, and single carriageways, with no context showing a robust reduction. In movement corridors where road geometry cues higher speeds, sign-only limits fail to self-enforce. These findings highlight a structural "wrong-road problem." Indiscriminate sign-only limits impose economic drag without proportionate safety returns. Transport authorities should move away from blanket statutory defaults and return to targeted physical engineering on high-harm corridors.
