  Obtaining high quality sensor information is critical in vehicular
emergencies. However, existing standards such as IEEE 802.11p/DSRC and LTE-A
cannot support either the required data rates or the latency requirements. One
solution to this problem is for municipalities to invest in dedicated base
stations to ensure that drivers have the information they need to make safe
decisions in or near accidents. In this paper we further propose that these
municipality-owned base stations form a Single Frequency Network (SFN). In
order to ensure that transmissions are reliable, we derive tight bounds on the
outage probability when the SFN is overlaid on an existing cellular network.
Using our bounds, we propose a transmission power allocation algorithm. We show
that our power allocation model can reduce the total instantaneous SFN
transmission power up to $20$ times compared to a static uniform power
allocation solution, for the considered scenarios. The result is particularly
important when base stations rely on an off-grid power source (i.e.,
batteries).
