Peak$-$hour traffic demand between an origin$-$destination pair is initially $3500$ vehicles. The two routes connecting the pair have performance functions $t_1=2+3(\frac{x_1}{c_1})$ and $t_2=4+2(\frac{x_2}{c_2}),$ where the t$\text{'}$s are travel times in minutes, the $x^{\text{'}}$ s are the peak$-$hour traffic volumes expressed in thousands, and the c$\text{'}$s are the peak$-$hour route capacities expressed in thousands of vehicles per hour. Initially, the capacities of routes $1$ and $2$ are $2500$ and $4000ve\frac{h}{h},$ respectively. A reconstruction project reduces capacity on route $2$ to $2000$ veh$/$h$.$ Assuming user equilibrium before and during reconstruction, what reduction in total peak$-$hour origindestination traffic flow is needed to ensure that total travel times $($summation of all $x_a{t}_a\text{'}$s$,$ where a denotes route$)$ during reconstruction are equal to those before reconstruction?Peak$-$hour traffic demand between an origin$-$destination pair is initially $3500$ vehicles. The two routes connecting the pair have performance functions $t_1=2+3(\frac{x_1}{c_1})$ and $t_2=4+2(\frac{x_2}{c_2}),$ where the t$\text{'}$s are travel times in minutes, the $x^{\text{'}}$ s are the peak$-$hour traffic volumes expressed in thousands, and the c$\text{'}$s are the peak$-$hour route capacities expressed in thousands of vehicles per hour. Initially, the capacities of routes $1$ and $2$ are $2500$ and $4000ve\frac{h}{h},$ respectively. A reconstruction project reduces capacity on route $2$ to $2000$ veh$/$h$.$ Assuming user equilibrium before and during reconstruction, what reduction in total peak$-$hour origindestination traffic flow is needed to ensure that total travel times $($summation of all $x_a{t}_a\text{'}$s$,$ where a denotes route$)$ during reconstruction are equal to those before reconstruction?