$2.$ Suppose that a traffic engineer knows that her vehicle detector turns on and off before the vehicle has completely crossed the detector. From experimental calibration of this detector, she has verified that the true length of a vehicle, $\backslash ($ L$\_\{$j$\}\backslash ),$ is always $\backslash (\backslash$varepsilon $\backslash )$ larger than its $($measured$)$ effective length $($independent of j$).$ She knows $\backslash (\backslash$varepsilon $\backslash ).$ She observes a flow, q$,$ and an effective occupancy $\backslash (\backslash$mathrm$\{$r$\}^\{*\}\backslash )$ from her detector. What else must she know in order to convert her $\backslash (\backslash$mathrm$\{$r$\}^\{*\}\backslash )$ into r so that she can compare her observations $($i$.$e$.,$ occupancies$)$ with those measured by another detector? The vehicles have different $\backslash ($ L$\_\{$j$\}\backslash )$ and different speeds, $\backslash (\backslash$mathrm$\{$v$\}\_\{\backslash$mathrm$\{$j$\}\}\backslash ).$