Here are some options:

\documentclass[twocolumn]{article}
\usepackage[paper=a5paper,margin=1cm]{geometry}% Just for this example
\usepackage{hyperref}
\def\UrlBreaks{\do\/\do-}
\begin{document}
Default bibliography:
\begin{thebibliography}{X}
\bibitem{abc0}
Adventech B+B SmartWorx. {\itshape Smart IoT Technologies for Adaptive
Traffic Management Using a Wireless Mesh Sensor Network.} 19 November 2014.
http://advantech-bb.com/smart-iot-technologies-for-adaptive-traffic-management-using-a-wireless-mesh-sensor-networks/.
Accessed: 15 October 2017.
\bibitem{def0}
Elsevier. {\itshape Data-driven smart-city-enabled traffic system modeling,
analysis and optimization.}
https://www.journals.elsevier.com/transportation-research-part-c-emerging-technologies/call-for-papers.
Accessed: 15 October 2017.
\end{thebibliography}
\newpage
First alternative:
\begin{thebibliography}{X}
\raggedright
\bibitem{abc1}
Adventech B+B SmartWorx. {\itshape Smart IoT Technologies for Adaptive
Traffic Management Using a Wireless Mesh Sensor Network.} 19 November 2014.
http://advantech-bb.com/smart-iot-technologies-for-adaptive-traffic-management-using-a-wireless-mesh-sensor-networks/.
Accessed: 15 October 2017.
\bibitem{def1}
Elsevier. {\itshape Data-driven smart-city-enabled traffic system modeling,
analysis and optimization.}
https://www.journals.elsevier.com/transportation-research-part-c-emerging-technologies/call-for-papers.
Accessed: 15 October 2017.
\end{thebibliography}
\newpage
Second alternative:
\begin{thebibliography}{X}
\bibitem{abc2}
Adventech B+B SmartWorx. {\itshape Smart IoT Technologies for Adaptive
Traffic Management Using a Wireless Mesh Sensor Network.} 19 November 2014.
\url{http://advantech-bb.com/smart-iot-technologies-for-adaptive-traffic-management-using-a-wireless-mesh-sensor-networks/}.
Accessed: 15 October 2017.
\bibitem{def2}
Elsevier. {\itshape Data-driven smart-city-enabled traffic system modeling,
analysis and optimization.}
\url{https://www.journals.elsevier.com/transportation-research-part-c-emerging-technologies/call-for-papers}.
Accessed: 15 October 2017.
\end{thebibliography}
\newpage
Third alternative:
\begin{thebibliography}{X}
\bibitem{abc3}
Adventech B+B SmartWorx. {\itshape Smart IoT Technologies for Adaptive
Traffic Management Using a Wireless Mesh Sensor Network.} 19 November 2014.
\href{http://advantech-bb.com/smart-iot-technologies-for-adaptive-traffic-management-using-a-wireless-mesh-sensor-networks/}{http://advantech-bb.com/}.
Accessed: 15 October 2017.
\bibitem{def3}
Elsevier. {\itshape Data-driven smart-city-enabled traffic system modeling,
analysis and optimization.}
\href{https://www.journals.elsevier.com/transportation-research-part-c-emerging-technologies/call-for-papers}{http://www.journals.elsevier.com/}.
Accessed: 15 October 2017.
\end{thebibliography}
\newpage
Fourth alternative:
\begin{thebibliography}{X}
\bibitem{abc4}
Adventech B+B SmartWorx. {\itshape Smart IoT Technologies for Adaptive
Traffic Management Using a Wireless Mesh Sensor Network.} 19 November 2014.
\href{http://advantech-bb.com/smart-iot-technologies-for-adaptive-traffic-management-using-a-wireless-mesh-sensor-networks/}{http://advantech-bb.com/}
Accessed: 15 October 2017.
\bibitem{def4}
Elsevier. {\itshape Data-driven smart-city-enabled traffic system modeling,
analysis and optimization.}
\href{https://www.journals.elsevier.com/transportation-research-part-c-emerging-technologies/call-for-papers}{https://www.journals.elsevier.com/}
Accessed: 15 October 2017.
\end{thebibliography}
\newpage
Fifth alternative:
\begin{thebibliography}{X}
\bibitem{abc5}
Adventech B+B SmartWorx. {\itshape Smart IoT Technologies for Adaptive
Traffic Management Using a Wireless Mesh Sensor Network.} 19 November 2014.
\href{http://advantech-bb.com/smart-iot-technologies-for-adaptive-traffic-management-using-a-wireless-mesh-sensor-networks/}{\ttfamily advantech-bb.com}
Accessed: 15 October 2017.
\bibitem{def5}
Elsevier. {\itshape Data-driven smart-city-enabled traffic system modeling,
analysis and optimization.}
\href{https://www.journals.elsevier.com/transportation-research-part-c-emerging-technologies/call-for-papers}{\ttfamily www.journals.elsevier.com}
Accessed: 15 October 2017.
\end{thebibliography}
\end{document}
In the above example,
The original input.
Using a \raggedright alignment within the thebibliography environment that helps with line-breaking. One could even consider using \RaggedRight from ragged2e.
Using url (also provided by hyperref) with addition line-breaking rules (see How to deal with bibliography items containing long URLs?).
Using abbreviated URLs with full-length embedded hyperlinks when viewing online.
Placing the URL on a line of its own, shortened if possible.
Mixing (3) and (4) above, together with a drop of the protocol and path in lieu of keeping only the domain.

Online viewers of the content can still click the URL to go to the intended target. Offline viewers should be able to find the content online by starting with the URL domain.
Another option to consider might be a URL shortner. While this may standardise your online references (lengths), there's not much to be gained by the casual paper reader from the online identify if a URL is not legible (that is, my.fancy.long.url provides more value than f.akeurl/1h3ial).
For additional information and a discussion on this topic (using similar techniques suggested above), see URLs: Some Practical Advice.
thebibliographyenvironment), correct? – Werner Oct 18 '17 at 02:45urlpackage gives good flexibility in creating breaks and allowing larger spaces around/characters if needed. – David Purton Oct 18 '17 at 05:35