## 5 Conclusions and Future Work  
Collisions between trains and vehicles make up a critical portion of train accidents in the U.S. The authors of [3; 4; 5] present that vehicular communication system-aided train crossing safety warning systems can reduce the number of collisions. Additionally, an infrastructure-aided system can provide a better warning performance than a direct warning from a train to a vehicle. Since the vehicular communication system uses the 5.9 GHz spectrum and the train-related communication link is different from the usual V2V or V2I link, the measurement, evaluation of the train track propagation channel, and the comparison between previously studied vehicular channels are needed. We conducted propagation channel measurements at several real-operating crossings of the SVRR railroad tracks. The PDP is generated from measured data, and we obtained channel characteristics from the PDP. We compared path loss with 3 GPP path loss models to evaluate the path loss exponent, Ricean K-factor, RMS delay, and Doppler spread. From the 3 GPP model comparison, RMA LoS or SMA or Uma NLoS models are preferred to use depending on the environment near the crossing. The evaluated path loss exponent values with an omnidirectional antenna are 2.61-2.95 for rural-like crossings and 3.05-4.11 for suburban-like crossings and with a bidirectional antenna are 2.17-2.34 for rural-like crossings and 2.50-3.67 for suburban-like crossings. The evaluated Ricean K-factor values with an omnidirectional antenna are 3.29-3.64 dB for rural-like crossings and 3.55-4.25 dB for suburban-like crossings and with a bidirectional antenna are 6.20-7.47 dB for rural-like crossings and 5.77-6.98 dB for suburban-like crossings. The evaluated RMS delays with an omnidirectional antenna are 177.69-212.85 us for rural-like crossings and 72.57-81.00 us for suburban-like crossings with a bidirectional antenna are 93.94-137.52 us \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multirow{2}{*}{**Stat**} & \multicolumn{6}{c}{**Omni**} & \multicolumn{6}{c}{**Bi**} \\ \cline{3-13}  & & \#1 & \#2 & \#3 & \#4 & \#5 & \#1 & \#2 & \#3 & \#4 & \#5 \\ \hline \multirow{3}{*}{K-factor} & \(\mu\) & 3.58 & 3.29 & 3.55 & 4.25 & 3.64 & 6.47 & 7.47 & 5.77 & 6.98 & 6.20 \\  & \(\sigma\) & 1.33 & 3.84 & 1.57 & 1.91 & 1.96 & 2.68 & 2.50 & 2.85 & 2.03 & 2.67 \\ \multirow{3}{*}{Path loss exponent} & \(\mu\) & 2.78 & 2.61 & 3.05 & 4.11 & 2.95 & 2.17 & 2.34 & 2.50 & 3.67 & 2.33 \\  & \(\sigma\) & 0.38 & 0.31 & 0.36 & 0.60 & 0.49 & 0.59 & 0.59 & 0.34 & 0.96 & 0.57 \\ \multirow{3}{*}{RMS delay} & \(\mu\) & 198.69 & 212.85 & 198.13 & 413.98 & 177.69 & 137.52 & 129.46 & 126.25 & 253.04 & 93.94 \\  & \(\sigma\) & 28.39 & 60.86 & 50.74 & 85.44 & 25.84 & 31.36 & 37.03 & 50.72 & 41.14 & 22.91 \\ \multirow{3}{*}{Doppler spread} & \(\mu\) & 47.99 & 53.31 & 81.00 & 72.57 & 61.22 & 44.71 & 40.74 & 43.16 & 42.49 & 40.78 \\  & \(\sigma\) & 7.11 & 8.72 & 12.79 & 23.22 & 9.30 & 3.51 & 6.82 & 4.68 & 7.38 & 6.93 \\ \multirow{3}{*}{Fitted Path loss equation} & \multicolumn{1}{c}{a} & 17.08 & 17.67 & 18.67 & 21.96 & 16.75 & 6.02 & 6.86 & 7.47 & 8.84 & 6.85 \\  & \multicolumn{1}{c}{(PL = a\cdot\text{log}_{10}\text{d}+\text{b})} & \multicolumn{1}{c}{b} & 67.11 & 63.05 & 66.51 & 77.77 & 70.50 & 73.78 & 80.00 & 77.13 & 94.52 & 77.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistics of propagation channel characteristics. for rural-like crossings and 126.25-253.04 us for suburban-like crossings. The evaluated Doppler spreads with an omnidirectional antenna are 47.99-61.22 Hz for rural-like crossings and 72.57-81.00 Hz for suburban-like crossings and with a bidirectional antenna are 40.74-44.71 Hz for rural-like crossings and 42.49-43.16 Hz for suburban-like crossings. From the evaluations, we can assume that a communication system using a bidirectional will be less affected by noise from the environment near the train tracks or crossings than when using an omnidirectional antenna.